Merge branch 'master' into BAEL-2775

.gitignore

@@ -19,6 +19,7 @@
 .idea/
 *.iml
 *.iws
+out/
 
 # Mac
 .DS_Store
@@ -27,6 +28,9 @@
 log/
 target/
 
+# Gradle
+.gradle/
+
 spring-openid/src/main/resources/application.properties
 .recommenders/
 /spring-hibernate4/nbproject/

akka-streams/pom.xml

@@ -14,18 +14,19 @@
     <dependencies>
         <dependency>
             <groupId>com.typesafe.akka</groupId>
-            <artifactId>akka-stream_2.11</artifactId>
+            <artifactId>akka-stream_${scala.version}</artifactId>
             <version>${akkastreams.version}</version>
         </dependency>
         <dependency>
             <groupId>com.typesafe.akka</groupId>
-            <artifactId>akka-stream-testkit_2.11</artifactId>
+            <artifactId>akka-stream-testkit_${scala.version}</artifactId>
             <version>${akkastreams.version}</version>
         </dependency>
     </dependencies>
 
     <properties>
         <akkastreams.version>2.5.2</akkastreams.version>
+        <scala.version>2.11</scala.version>
     </properties>
 
 </project>

algorithms-miscellaneous-1/README.md

@@ -14,7 +14,5 @@
 - [Calculate Factorial in Java](https://www.baeldung.com/java-calculate-factorial)
 - [Find Substrings That Are Palindromes in Java](https://www.baeldung.com/java-palindrome-substrings)
 - [Find the Longest Substring without Repeating Characters](https://www.baeldung.com/java-longest-substring-without-repeated-characters)
-- [Java Two Pointer Technique](https://www.baeldung.com/java-two-pointer-technique)
 - [Permutations of an Array in Java](https://www.baeldung.com/java-array-permutations)
-- [Implementing Simple State Machines with Java Enums](https://www.baeldung.com/java-enum-simple-state-machine)
 - [Generate Combinations in Java](https://www.baeldung.com/java-combinations-algorithm)

algorithms-miscellaneous-2/README.md

@@ -8,9 +8,6 @@
 - [Create a Sudoku Solver in Java](http://www.baeldung.com/java-sudoku)
 - [Displaying Money Amounts in Words](http://www.baeldung.com/java-money-into-words)
 - [A Collaborative Filtering Recommendation System in Java](http://www.baeldung.com/java-collaborative-filtering-recommendations)
-- [Converting Between Roman and Arabic Numerals in Java](http://www.baeldung.com/java-convert-roman-arabic)
-- [Practical Java Examples of the Big O Notation](http://www.baeldung.com/java-algorithm-complexity)
-- [An Introduction to the Theory of Big-O Notation](http://www.baeldung.com/big-o-notation)
 - [Check If Two Rectangles Overlap In Java](https://www.baeldung.com/java-check-if-two-rectangles-overlap)
 - [Calculate the Distance Between Two Points in Java](https://www.baeldung.com/java-distance-between-two-points)
 - [Find the Intersection of Two Lines in Java](https://www.baeldung.com/java-intersection-of-two-lines)

algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/relativelyprime/RelativelyPrime.java

@@ -0,0 +1,45 @@
+package com.baeldung.algorithms.relativelyprime;
+
+import java.math.BigInteger;
+
+class RelativelyPrime {
+
+    static boolean iterativeRelativelyPrime(int a, int b) {
+        return iterativeGCD(a, b) == 1;
+    }
+
+    static boolean recursiveRelativelyPrime(int a, int b) {
+        return recursiveGCD(a, b) == 1;
+    }
+
+    static boolean bigIntegerRelativelyPrime(int a, int b) {
+        return BigInteger.valueOf(a).gcd(BigInteger.valueOf(b)).equals(BigInteger.ONE);
+    }
+
+    private static int iterativeGCD(int a, int b) {
+        int tmp;
+        while (b != 0) {
+            if (a < b) {
+                tmp = a;
+                a = b;
+                b = tmp;
+            }
+            tmp = b;
+            b = a % b;
+            a = tmp;
+        }
+        return a;
+    }
+
+    private static int recursiveGCD(int a, int b) {
+        if (b == 0) {
+            return a;
+        }
+        if (a < b) {
+            return recursiveGCD(b, a);
+        }
+        return recursiveGCD(b, a % b);
+    }
+
+
+}

algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/reversingtree/TreeNode.java

@@ -1,42 +1,42 @@
-package com.baeldung.algorithms.reversingtree;
-
-public class TreeNode {
-
-    private int value;
-    private TreeNode rightChild;
-    private TreeNode leftChild;
-
-    public int getValue() {
-        return value;
-    }
-
-    public void setValue(int value) {
-        this.value = value;
-    }
-
-    public TreeNode getRightChild() {
-        return rightChild;
-    }
-
-    public void setRightChild(TreeNode rightChild) {
-        this.rightChild = rightChild;
-    }
-
-    public TreeNode getLeftChild() {
-        return leftChild;
-    }
-
-    public void setLeftChild(TreeNode leftChild) {
-        this.leftChild = leftChild;
-    }
-
-    public TreeNode(int value, TreeNode rightChild, TreeNode leftChild) {
-        this.value = value;
-        this.rightChild = rightChild;
-        this.leftChild = leftChild;
-    }
-
-    public TreeNode(int value) {
-        this.value = value;
-    }
-}
+package com.baeldung.algorithms.reversingtree;
+
+public class TreeNode {
+
+    private int value;
+    private TreeNode rightChild;
+    private TreeNode leftChild;
+
+    public int getValue() {
+        return value;
+    }
+
+    public void setValue(int value) {
+        this.value = value;
+    }
+
+    public TreeNode getRightChild() {
+        return rightChild;
+    }
+
+    public void setRightChild(TreeNode rightChild) {
+        this.rightChild = rightChild;
+    }
+
+    public TreeNode getLeftChild() {
+        return leftChild;
+    }
+
+    public void setLeftChild(TreeNode leftChild) {
+        this.leftChild = leftChild;
+    }
+
+    public TreeNode(int value, TreeNode leftChild, TreeNode rightChild) {
+        this.value = value;
+        this.rightChild = rightChild;
+        this.leftChild = leftChild;
+    }
+
+    public TreeNode(int value) {
+        this.value = value;
+    }
+}

algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/reversingtree/TreeReverser.java

@@ -1,68 +1,53 @@
-package com.baeldung.algorithms.reversingtree;
-
-import java.util.LinkedList;
-
-public class TreeReverser {
-
-    public TreeNode createBinaryTree() {
-
-        TreeNode leaf1 = new TreeNode(3);
-        TreeNode leaf2 = new TreeNode(1);
-        TreeNode leaf3 = new TreeNode(9);
-        TreeNode leaf4 = new TreeNode(6);
-
-        TreeNode nodeLeft = new TreeNode(2, leaf1, leaf2);
-        TreeNode nodeRight = new TreeNode(7, leaf3, leaf4);
-
-        TreeNode root = new TreeNode(4, nodeRight, nodeLeft);
-
-        return root;
-    }
-
-    public void reverseRecursive(TreeNode treeNode) {
-        if (treeNode == null) {
-            return;
-        }
-
-        TreeNode temp = treeNode.getLeftChild();
-        treeNode.setLeftChild(treeNode.getRightChild());
-        treeNode.setRightChild(temp);
-
-        reverseRecursive(treeNode.getLeftChild());
-        reverseRecursive(treeNode.getRightChild());
-    }
-
-    public void reverseIterative(TreeNode treeNode) {
-        LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
-
-        if (treeNode != null) {
-            queue.add(treeNode);
-        }
-
-        while (!queue.isEmpty()) {
-
-            TreeNode node = queue.poll();
-            if (node.getLeftChild() != null)
-                queue.add(node.getLeftChild());
-            if (node.getRightChild() != null)
-                queue.add(node.getRightChild());
-
-            TreeNode temp = node.getLeftChild();
-            node.setLeftChild(node.getRightChild());
-            node.setRightChild(temp);
-        }
-    }
-
-    public String toString(TreeNode root) {
-        if (root == null) {
-            return "";
-        }
-
-        StringBuffer buffer = new StringBuffer(String.valueOf(root.getValue())).append(" ");
-
-        buffer.append(toString(root.getLeftChild()));
-        buffer.append(toString(root.getRightChild()));
-
-        return buffer.toString();
-    }
-}
+package com.baeldung.algorithms.reversingtree;
+
+import java.util.LinkedList;
+
+public class TreeReverser {
+
+    public void reverseRecursive(TreeNode treeNode) {
+        if (treeNode == null) {
+            return;
+        }
+
+        TreeNode temp = treeNode.getLeftChild();
+        treeNode.setLeftChild(treeNode.getRightChild());
+        treeNode.setRightChild(temp);
+
+        reverseRecursive(treeNode.getLeftChild());
+        reverseRecursive(treeNode.getRightChild());
+    }
+
+    public void reverseIterative(TreeNode treeNode) {
+        LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
+
+        if (treeNode != null) {
+            queue.add(treeNode);
+        }
+
+        while (!queue.isEmpty()) {
+
+            TreeNode node = queue.poll();
+            if (node.getLeftChild() != null)
+                queue.add(node.getLeftChild());
+            if (node.getRightChild() != null)
+                queue.add(node.getRightChild());
+
+            TreeNode temp = node.getLeftChild();
+            node.setLeftChild(node.getRightChild());
+            node.setRightChild(temp);
+        }
+    }
+
+    public String toString(TreeNode root) {
+        if (root == null) {
+            return "";
+        }
+
+        StringBuffer buffer = new StringBuffer(String.valueOf(root.getValue())).append(" ");
+
+        buffer.append(toString(root.getLeftChild()));
+        buffer.append(toString(root.getRightChild()));
+
+        return buffer.toString();
+    }
+}

algorithms-miscellaneous-2/src/test/java/com/baeldung/algorithms/relativelyprime/RelativelyPrimeUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.algorithms.relativelyprime;
+
+import org.junit.Test;
+
+import static com.baeldung.algorithms.relativelyprime.RelativelyPrime.*;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class RelativelyPrimeUnitTest {
+
+    @Test
+    public void givenNonRelativelyPrimeNumbers_whenCheckingIteratively_shouldReturnFalse() {
+
+        boolean result = iterativeRelativelyPrime(45, 35);
+        assertThat(result).isFalse();
+    }
+
+    @Test
+    public void givenRelativelyPrimeNumbers_whenCheckingIteratively_shouldReturnTrue() {
+
+        boolean result = iterativeRelativelyPrime(500, 501);
+        assertThat(result).isTrue();
+    }
+
+    @Test
+    public void givenNonRelativelyPrimeNumbers_whenCheckingRecursively_shouldReturnFalse() {
+
+        boolean result = recursiveRelativelyPrime(45, 35);
+        assertThat(result).isFalse();
+    }
+
+    @Test
+    public void givenRelativelyPrimeNumbers_whenCheckingRecursively_shouldReturnTrue() {
+
+        boolean result = recursiveRelativelyPrime(500, 501);
+        assertThat(result).isTrue();
+    }
+
+    @Test
+    public void givenNonRelativelyPrimeNumbers_whenCheckingUsingBigIntegers_shouldReturnFalse() {
+
+        boolean result = bigIntegerRelativelyPrime(45, 35);
+        assertThat(result).isFalse();
+    }
+
+    @Test
+    public void givenRelativelyPrimeNumbers_whenCheckingBigIntegers_shouldReturnTrue() {
+
+        boolean result = bigIntegerRelativelyPrime(500, 501);
+        assertThat(result).isTrue();
+    }
+}

algorithms-miscellaneous-2/src/test/java/com/baeldung/algorithms/reversingtree/TreeReverserUnitTest.java

@@ -1,33 +1,47 @@
-package com.baeldung.algorithms.reversingtree;
-
-import static org.junit.jupiter.api.Assertions.assertEquals;
-
-import org.junit.jupiter.api.Test;
-
-public class TreeReverserUnitTest {
-
-    @Test
-    public void givenTreeWhenReversingRecursivelyThenReversed() {
-        TreeReverser reverser = new TreeReverser();
-
-        TreeNode treeNode = reverser.createBinaryTree();
-
-        reverser.reverseRecursive(treeNode);
-
-        assertEquals("4 7 9 6 2 3 1", reverser.toString(treeNode)
-            .trim());
-    }
-
-    @Test
-    public void givenTreeWhenReversingIterativelyThenReversed() {
-        TreeReverser reverser = new TreeReverser();
-
-        TreeNode treeNode = reverser.createBinaryTree();
-
-        reverser.reverseIterative(treeNode);
-
-        assertEquals("4 7 9 6 2 3 1", reverser.toString(treeNode)
-            .trim());
-    }
-
-}
+package com.baeldung.algorithms.reversingtree;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class TreeReverserUnitTest {
+
+    @Test
+    public void givenTreeWhenReversingRecursivelyThenReversed() {
+        TreeReverser reverser = new TreeReverser();
+
+        TreeNode treeNode = createBinaryTree();
+
+        reverser.reverseRecursive(treeNode);
+
+        assertEquals("4 7 9 6 2 3 1", reverser.toString(treeNode)
+            .trim());
+    }
+
+    @Test
+    public void givenTreeWhenReversingIterativelyThenReversed() {
+        TreeReverser reverser = new TreeReverser();
+
+        TreeNode treeNode = createBinaryTree();
+
+        reverser.reverseIterative(treeNode);
+
+        assertEquals("4 7 9 6 2 3 1", reverser.toString(treeNode)
+            .trim());
+    }
+
+    private TreeNode createBinaryTree() {
+
+        TreeNode leaf1 = new TreeNode(1);
+        TreeNode leaf2 = new TreeNode(3);
+        TreeNode leaf3 = new TreeNode(6);
+        TreeNode leaf4 = new TreeNode(9);
+
+        TreeNode nodeRight = new TreeNode(7, leaf3, leaf4);
+        TreeNode nodeLeft = new TreeNode(2, leaf1, leaf2);
+
+        TreeNode root = new TreeNode(4, nodeLeft, nodeRight);
+
+        return root;
+    }
+}

algorithms-miscellaneous-3/.gitignore

@@ -0,0 +1,4 @@
+/target/
+.settings/
+.classpath
+.project

algorithms-miscellaneous-3/README.md

@@ -0,0 +1,7 @@
+## Relevant articles:
+
+- [Java Two Pointer Technique](https://www.baeldung.com/java-two-pointer-technique)
+- [Implementing Simple State Machines with Java Enums](https://www.baeldung.com/java-enum-simple-state-machine)
+- [Converting Between Roman and Arabic Numerals in Java](http://www.baeldung.com/java-convert-roman-arabic)
+- [Practical Java Examples of the Big O Notation](http://www.baeldung.com/java-algorithm-complexity)
+- [An Introduction to the Theory of Big-O Notation](http://www.baeldung.com/big-o-notation)

algorithms-miscellaneous-3/pom.xml

@@ -0,0 +1,39 @@
+<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>
+    <artifactId>algorithms-miscellaneous-3</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>algorithms-miscellaneous-3</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${org.assertj.core.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <pluginManagement>
+            <plugins>
+                <plugin>
+                    <groupId>org.codehaus.mojo</groupId>
+                    <artifactId>exec-maven-plugin</artifactId>
+                    <version>${exec-maven-plugin.version}</version>
+                </plugin>
+            </plugins>
+        </pluginManagement>
+    </build>
+
+    <properties>
+        <org.assertj.core.version>3.9.0</org.assertj.core.version>
+    </properties>
+
+</project>

antlr/pom.xml

@@ -10,6 +10,14 @@
         <version>1.0.0-SNAPSHOT</version>
     </parent>
 
+    <dependencies>
+        <dependency>
+            <groupId>org.antlr</groupId>
+            <artifactId>antlr4-runtime</artifactId>
+            <version>${antlr.version}</version>
+        </dependency>
+    </dependencies>
+
     <build>
         <plugins>
             <plugin>
@@ -44,13 +52,7 @@
             </plugin>
         </plugins>
     </build>
-    <dependencies>
-        <dependency>
-            <groupId>org.antlr</groupId>
-            <artifactId>antlr4-runtime</artifactId>
-            <version>${antlr.version}</version>
-        </dependency>
-    </dependencies>
+    	
     <properties>
         <antlr.version>4.7.1</antlr.version>
         <mojo.version>3.0.0</mojo.version>

apache-cxf/sse-jaxrs/sse-jaxrs-client/pom.xml

@@ -12,9 +12,18 @@
         <version>0.0.1-SNAPSHOT</version>
     </parent>
 
-    <properties>
-        <cxf-version>3.2.0</cxf-version>
-    </properties>
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.cxf</groupId>
+            <artifactId>cxf-rt-rs-client</artifactId>
+            <version>${cxf-version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.cxf</groupId>
+            <artifactId>cxf-rt-rs-sse</artifactId>
+            <version>${cxf-version}</version>
+        </dependency>
+    </dependencies>
 
     <build>
         <plugins>
@@ -45,17 +54,8 @@
         </plugins>
     </build>
 
-    <dependencies>
-        <dependency>
-            <groupId>org.apache.cxf</groupId>
-            <artifactId>cxf-rt-rs-client</artifactId>
-            <version>${cxf-version}</version>
-        </dependency>
-        <dependency>
-            <groupId>org.apache.cxf</groupId>
-            <artifactId>cxf-rt-rs-sse</artifactId>
-            <version>${cxf-version}</version>
-        </dependency>
-    </dependencies>
+    <properties>
+        <cxf-version>3.2.0</cxf-version>
+    </properties>
 
 </project>

apache-cxf/sse-jaxrs/sse-jaxrs-server/pom.xml

@@ -13,11 +13,28 @@
         <version>0.0.1-SNAPSHOT</version>
     </parent>
 
-    <properties>
-        <liberty-maven-plugin.version>2.4.2</liberty-maven-plugin.version>
-        <failOnMissingWebXml>false</failOnMissingWebXml>
-        <openliberty-version>18.0.0.2</openliberty-version>
-    </properties>
+    <dependencies>
+
+        <dependency>
+            <groupId>javax.ws.rs</groupId>
+            <artifactId>javax.ws.rs-api</artifactId>
+            <version>2.1</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>javax.enterprise</groupId>
+            <artifactId>cdi-api</artifactId>
+            <version>2.0</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>javax.json.bind</groupId>
+            <artifactId>javax.json.bind-api</artifactId>
+            <version>1.0</version>
+            <scope>provided</scope>
+        </dependency>
+
+    </dependencies>
 
     <build>
         <finalName>${project.artifactId}</finalName>
@@ -59,27 +76,10 @@
         </plugins>
     </build>
 
-    <dependencies>
-
-        <dependency>
-            <groupId>javax.ws.rs</groupId>
-            <artifactId>javax.ws.rs-api</artifactId>
-            <version>2.1</version>
-            <scope>provided</scope>
-        </dependency>
-        <dependency>
-            <groupId>javax.enterprise</groupId>
-            <artifactId>cdi-api</artifactId>
-            <version>2.0</version>
-            <scope>provided</scope>
-        </dependency>
-        <dependency>
-            <groupId>javax.json.bind</groupId>
-            <artifactId>javax.json.bind-api</artifactId>
-            <version>1.0</version>
-            <scope>provided</scope>
-        </dependency>
-
-    </dependencies>
+    <properties>
+        <liberty-maven-plugin.version>2.4.2</liberty-maven-plugin.version>
+        <failOnMissingWebXml>false</failOnMissingWebXml>
+        <openliberty-version>18.0.0.2</openliberty-version>
+    </properties>
 
 </project>

apache-fop/README.md

@@ -3,7 +3,3 @@
 ## Core Java Cookbooks and Examples
 
 ### Relevant Articles: 
-- [Immutable ArrayList in Java](http://www.baeldung.com/java-immutable-list)
-- [Java - Reading a Large File Efficiently](http://www.baeldung.com/java-read-lines-large-file)
-- [Java InputStream to String](http://www.baeldung.com/convert-input-stream-to-string)
-

apache-meecrowave/pom.xml

@@ -6,6 +6,12 @@
     <version>0.0.1</version>
     <name>apache-meecrowave</name>
     <description>A sample REST API application with Meecrowave</description>
+    
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
 
     <dependencies>
         <!-- https://mvnrepository.com/artifact/org.apache.meecrowave/meecrowave-core -->

apache-meecrowave/src/test/java/com/baeldung/meecrowave/ArticleEndpointsUnitTest.java

@@ -17,7 +17,7 @@ import okhttp3.Request;
 import okhttp3.Response;
 
 @RunWith(MonoMeecrowave.Runner.class)
-public class ArticleEndpointsTest {
+public class ArticleEndpointsUnitTest {
     
     @ConfigurationInject
     private Meecrowave.Builder config;

autovalue/src/main/java/com/baeldung/autofactory/provided/IntermediateAssembler.java

@@ -1,8 +1,9 @@
 package com.baeldung.autofactory.provided;
 
+import com.baeldung.autofactory.model.Camera;
 import com.google.auto.factory.AutoFactory;
 import com.google.auto.factory.Provided;
-import javafx.scene.Camera;
+
 
 import javax.inject.Provider;
 

azure/README.md

@@ -1,4 +1,4 @@
 ### Relevant Articles:
 
-- [Deploy Spring Boot App to Azure](http://www.baeldung.com/spring-boot-azure)
+- [Deploy a Spring Boot App to Azure](http://www.baeldung.com/spring-boot-azure)
 

blade/README.md

@@ -1,5 +1,5 @@
 ### Relevant Articles: 
 
-- [Blade - A Complete GuideBook](http://www.baeldung.com/blade) 
+- [Blade – A Complete Guidebook](http://www.baeldung.com/blade) 
 
-Run Integration Tests with `mvn integration-test`
+Run Integration Tests with `mvn integration-test`

cloud-foundry-uaa/README.md

@@ -0,0 +1,3 @@
+### Revelant Articles
+
+- [A Quick Guide To Using Cloud Foundry UAA](https://www.baeldung.com/cloud-foundry-uaa)

cloud-foundry-uaa/cf-uaa-config/uaa.yml

@@ -1,12 +1,7 @@
 issuer:
   uri: http://localhost:8080/uaa
 
-spring_profiles: postgresql,default  
-  
-database.driverClassName: org.postgresql.Driver
-database.url: jdbc:postgresql:uaadb2
-database.username: postgres
-database.password: postgres  
+spring_profiles: default,hsqldb
   
 encryption:
   active_key_label: CHANGE-THIS-KEY

cloud-foundry-uaa/cf-uaa-oauth2-client/pom.xml

@@ -2,24 +2,20 @@
 <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>
-        <groupId>org.springframework.boot</groupId>
-        <artifactId>spring-boot-starter-parent</artifactId>
-        <version>2.1.3.RELEASE</version>
-        <relativePath/> <!-- lookup parent from repository -->
-    </parent>
     <groupId>com.example</groupId>
     <artifactId>cf-uaa-oauth2-client</artifactId>
     <version>0.0.1-SNAPSHOT</version>
     <name>uaa-client-webapp</name>
     <description>Demo project for Spring Boot</description>
 
-    <properties>
-        <java.version>1.8</java.version>
-    </properties>
+    <parent>
+        <artifactId>parent-boot-2</artifactId>
+        <groupId>com.baeldung</groupId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-boot-2</relativePath>
+    </parent>
 
     <dependencies>
-
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-web</artifactId>
@@ -28,7 +24,6 @@
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-oauth2-client</artifactId>
         </dependency>
-
     </dependencies>
 
     <build>
@@ -40,4 +35,7 @@
         </plugins>
     </build>
 
+    <properties>
+        <java.version>1.8</java.version>
+    </properties>
 </project>

cloud-foundry-uaa/cf-uaa-oauth2-client/src/main/resources/application.properties

@@ -1,23 +1,11 @@
-# SECURITY OAUTH2 CLIENT (OAuth2ClientProperties)
-#spring.security.oauth2.client.provider.*= # OAuth provider details.
-#spring.security.oauth2.client.registration.*= # OAuth client registrations.
-
 server.port=8081
-#server.servlet.context-path=/uaa-client-webapp
 
-uaa.url=http://localhost:8080/uaa
 resource.server.url=http://localhost:8082
 
-spring.security.oauth2.client.registration.uaa.client-name=UAA OAuth2 Client
-spring.security.oauth2.client.registration.uaa.client-id=client1
-spring.security.oauth2.client.registration.uaa.client-secret=client1
-spring.security.oauth2.client.registration.uaa.authorization-grant-type=authorization_code
+spring.security.oauth2.client.registration.uaa.client-name=Web App Client
+spring.security.oauth2.client.registration.uaa.client-id=webappclient
+spring.security.oauth2.client.registration.uaa.client-secret=webappclientsecret
 spring.security.oauth2.client.registration.uaa.scope=resource.read,resource.write,openid,profile
-spring.security.oauth2.client.registration.uaa.redirect-uri=http://localhost:8081/login/oauth2/code/uaa
-#spring.security.oauth2.client.registration.uaa.redirect-uri=http://localhost:8081/**
 
-spring.security.oauth2.client.provider.uaa.token-uri=${uaa.url}/oauth/token
-spring.security.oauth2.client.provider.uaa.authorization-uri=${uaa.url}/oauth/authorize
-spring.security.oauth2.client.provider.uaa.jwk-set-uri=${uaa.url}/token_keys
-spring.security.oauth2.client.provider.uaa.user-info-uri=${uaa.url}/userinfo
-spring.security.oauth2.client.provider.uaa.user-name-attribute=user_name
+spring.security.oauth2.client.provider.uaa.issuer-uri=http://localhost:8080/uaa/oauth/token
+

cloud-foundry-uaa/cf-uaa-oauth2-resource-server/pom.xml

@@ -2,24 +2,20 @@
 <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>
-        <groupId>org.springframework.boot</groupId>
-        <artifactId>spring-boot-starter-parent</artifactId>
-        <version>2.1.3.RELEASE</version>
-        <relativePath/> <!-- lookup parent from repository -->
-    </parent>
     <groupId>com.baeldung.cfuaa</groupId>
     <artifactId>cf-uaa-oauth2-resource-server</artifactId>
     <version>0.0.1-SNAPSHOT</version>
     <name>cf-uaa-oauth2-resource-server</name>
     <description>Demo project for Spring Boot</description>
 
-    <properties>
-        <java.version>1.8</java.version>
-    </properties>
-
+    <parent>
+        <artifactId>parent-boot-2</artifactId>
+        <groupId>com.baeldung</groupId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-boot-2</relativePath>
+    </parent>
+	
     <dependencies>
-
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-oauth2-resource-server</artifactId>
@@ -28,7 +24,6 @@
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-web</artifactId>
         </dependency>
-
     </dependencies>
 
     <build>
@@ -40,4 +35,8 @@
         </plugins>
     </build>
 
+    <properties>
+        <java.version>1.8</java.version>
+    </properties>
+
 </project>

cloud-foundry-uaa/cf-uaa-oauth2-resource-server/src/main/resources/application.properties

@@ -1,16 +1,3 @@
 server.port=8082
 
-uaa.url=http://localhost:8080/uaa
-
-#approch1
-spring.security.oauth2.resourceserver.jwt.issuer-uri=${uaa.url}/oauth/token
-
-#approch2
-#spring.security.oauth2.resourceserver.jwt.jwk-set-uri=${uaa.url}/token_key
-
-# SECURITY OAUTH2 CLIENT (OAuth2ClientProperties)
-#security.oauth2.client.client-id=client1
-#security.oauth2.client.client-secret=client1
-
-#security.oauth2.resource.jwt.key-uri=${uaa.url}/token_key
-#security.oauth2.resource.token-info-uri=${uaa.url}/oauth/check_token
+spring.security.oauth2.resourceserver.jwt.issuer-uri=http://localhost:8080/uaa/oauth/token

core-groovy-2/README.md

@@ -0,0 +1,7 @@
+# Groovy
+
+## Relevant articles:
+
+- [String Matching in Groovy](http://www.baeldung.com/)
+- [Groovy def Keyword]
+

core-groovy-2/pom.xml

@@ -0,0 +1,131 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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>
+    <artifactId>core-groovy-2</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <name>core-groovy-2</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.codehaus.groovy</groupId>
+            <artifactId>groovy</artifactId>
+            <version>${groovy.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.codehaus.groovy</groupId>
+            <artifactId>groovy-all</artifactId>
+            <version>${groovy-all.version}</version>
+            <type>pom</type>
+        </dependency>
+        <dependency>
+            <groupId>org.codehaus.groovy</groupId>
+            <artifactId>groovy-dateutil</artifactId>
+            <version>${groovy.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.codehaus.groovy</groupId>
+            <artifactId>groovy-sql</artifactId>
+            <version>${groovy-sql.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.platform</groupId>
+            <artifactId>junit-platform-runner</artifactId>
+            <version>${junit.platform.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.hsqldb</groupId>
+            <artifactId>hsqldb</artifactId>
+            <version>${hsqldb.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.spockframework</groupId>
+            <artifactId>spock-core</artifactId>
+            <version>${spock-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.codehaus.gmavenplus</groupId>
+                <artifactId>gmavenplus-plugin</artifactId>
+                <version>${gmavenplus-plugin.version}</version>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>addSources</goal>
+                            <goal>addTestSources</goal>
+                            <goal>compile</goal>
+                            <goal>compileTests</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <artifactId>maven-failsafe-plugin</artifactId>
+                <version>${maven-failsafe-plugin.version}</version>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.junit.platform</groupId>
+                        <artifactId>junit-platform-surefire-provider</artifactId>
+                        <version>${junit.platform.version}</version>
+                    </dependency>
+                </dependencies>
+                <executions>
+                    <execution>
+                        <id>junit5</id>
+                        <goals>
+                            <goal>integration-test</goal>
+                            <goal>verify</goal>
+                        </goals>
+                        <configuration>
+                            <includes>
+                                <include>**/*Test5.java</include>
+                            </includes>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>2.20.1</version>
+                <configuration>
+                <useFile>false</useFile>
+                <includes>
+                    <include>**/*Test.java</include>
+                    <include>**/*Spec.java</include>
+                </includes>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <repositories>
+        <repository>
+            <id>central</id>
+            <url>http://jcenter.bintray.com</url>
+        </repository>
+    </repositories>
+
+    <properties>
+        <junit.platform.version>1.0.0</junit.platform.version>
+        <groovy.version>2.5.6</groovy.version>
+        <groovy-all.version>2.5.6</groovy-all.version>
+        <groovy-sql.version>2.5.6</groovy-sql.version>
+        <hsqldb.version>2.4.0</hsqldb.version>
+        <spock-core.version>1.1-groovy-2.4</spock-core.version>
+        <gmavenplus-plugin.version>1.6</gmavenplus-plugin.version>
+    </properties>
+</project>
+

core-groovy-2/src/test/groovy/com/baeldung/defkeyword/DefUnitTest.groovy

@@ -0,0 +1,79 @@
+package com.baeldung.defkeyword
+
+import org.codehaus.groovy.runtime.NullObject
+import org.codehaus.groovy.runtime.typehandling.GroovyCastException
+
+import groovy.transform.TypeChecked
+import groovy.transform.TypeCheckingMode
+
+@TypeChecked
+class DefUnitTest extends GroovyTestCase {
+    
+    def id
+    def firstName = "Samwell"
+    def listOfCountries = ['USA', 'UK', 'FRANCE', 'INDIA']
+    
+    @TypeChecked(TypeCheckingMode.SKIP)
+    def multiply(x, y) {
+        return x*y
+    }
+        
+    @TypeChecked(TypeCheckingMode.SKIP)
+    void testDefVariableDeclaration() {
+        
+        def list
+        assert list.getClass() == org.codehaus.groovy.runtime.NullObject
+        assert list.is(null)
+        
+        list = [1,2,4]
+        assert list instanceof ArrayList
+    }
+    
+    @TypeChecked(TypeCheckingMode.SKIP)
+    void testTypeVariables() {   
+        int rate = 200
+        try {
+            rate = [12] //GroovyCastException
+            rate = "nill" //GroovyCastException
+        } catch(GroovyCastException) {
+            println "Cannot assign anything other than integer"
+        }
+    }
+     
+    @TypeChecked(TypeCheckingMode.SKIP)
+    void testDefVariableMultipleAssignment() {
+        def rate
+        assert rate == null
+        assert rate.getClass() == org.codehaus.groovy.runtime.NullObject
+        
+        rate = 12
+        assert rate instanceof Integer
+        
+        rate = "Not Available"
+        assert rate instanceof String
+        
+        rate = [1, 4]
+        assert rate instanceof List
+        
+        assert divide(12, 3) instanceof BigDecimal
+        assert divide(1, 0) instanceof String
+
+    }
+    
+    def divide(int x, int y) {
+        if(y==0) {
+            return "Should not divide by 0"
+        } else {
+            return x/y
+        }
+    }
+    
+    def greetMsg() {
+        println "Hello! I am Groovy"
+    }
+    
+    void testDefVsType() {
+        def int count
+        assert count instanceof Integer
+    }
+}

core-groovy-2/src/test/groovy/com/baeldung/strings/StringMatchingSpec.groovy

@@ -0,0 +1,44 @@
+package com.baeldung.strings
+
+import spock.lang.Specification
+
+import java.util.regex.Pattern
+
+class StringMatchingSpec extends Specification {
+
+    def "pattern operator example"() {
+        given: "a pattern"
+        def p = ~'foo'
+
+        expect:
+        p instanceof Pattern
+
+        and: "you can use slash strings to avoid escaping of blackslash"
+        def digitPattern = ~/\d*/
+        digitPattern.matcher('4711').matches()
+    }
+
+    def "match operator example"() {
+        expect:
+        'foobar' ==~ /.*oba.*/
+
+        and: "matching is strict"
+        !('foobar' ==~ /foo/)
+    }
+
+    def "find operator example"() {
+        when: "using the find operator"
+        def matcher = 'foo and bar, baz and buz' =~ /(\w+) and (\w+)/
+
+        then: "will find groups"
+        matcher.size() == 2
+
+        and: "can access groups using array"
+        matcher[0][0] == 'foo and bar'
+        matcher[1][2] == 'buz'
+
+        and: "you can use it as a predicate"
+        'foobarbaz' =~ /bar/
+    }
+
+}

core-groovy-collections/README.md

@@ -0,0 +1,6 @@
+# Groovy
+
+## Relevant articles:
+
+- [Maps in Groovy](http://www.baeldung.com/)
+

core-groovy-collections/pom.xml

@@ -0,0 +1,131 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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>
+    <artifactId>core-groovy-collections</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <name>core-groovy-collections</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.codehaus.groovy</groupId>
+            <artifactId>groovy</artifactId>
+            <version>${groovy.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.codehaus.groovy</groupId>
+            <artifactId>groovy-all</artifactId>
+            <version>${groovy-all.version}</version>
+            <type>pom</type>
+        </dependency>
+        <dependency>
+            <groupId>org.codehaus.groovy</groupId>
+            <artifactId>groovy-dateutil</artifactId>
+            <version>${groovy.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.codehaus.groovy</groupId>
+            <artifactId>groovy-sql</artifactId>
+            <version>${groovy-sql.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.platform</groupId>
+            <artifactId>junit-platform-runner</artifactId>
+            <version>${junit.platform.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.hsqldb</groupId>
+            <artifactId>hsqldb</artifactId>
+            <version>${hsqldb.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.spockframework</groupId>
+            <artifactId>spock-core</artifactId>
+            <version>${spock-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.codehaus.gmavenplus</groupId>
+                <artifactId>gmavenplus-plugin</artifactId>
+                <version>${gmavenplus-plugin.version}</version>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>addSources</goal>
+                            <goal>addTestSources</goal>
+                            <goal>compile</goal>
+                            <goal>compileTests</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <artifactId>maven-failsafe-plugin</artifactId>
+                <version>${maven-failsafe-plugin.version}</version>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.junit.platform</groupId>
+                        <artifactId>junit-platform-surefire-provider</artifactId>
+                        <version>${junit.platform.version}</version>
+                    </dependency>
+                </dependencies>
+                <executions>
+                    <execution>
+                        <id>junit5</id>
+                        <goals>
+                            <goal>integration-test</goal>
+                            <goal>verify</goal>
+                        </goals>
+                        <configuration>
+                            <includes>
+                                <include>**/*Test5.java</include>
+                            </includes>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>2.20.1</version>
+                <configuration>
+                <useFile>false</useFile>
+                <includes>
+                    <include>**/*Test.java</include>
+                    <include>**/*Spec.java</include>
+                </includes>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <repositories>
+        <repository>
+            <id>central</id>
+            <url>http://jcenter.bintray.com</url>
+        </repository>
+    </repositories>
+
+    <properties>
+        <junit.platform.version>1.0.0</junit.platform.version>
+        <groovy.version>2.5.6</groovy.version>
+        <groovy-all.version>2.5.6</groovy-all.version>
+        <groovy-sql.version>2.5.6</groovy-sql.version>
+        <hsqldb.version>2.4.0</hsqldb.version>
+        <spock-core.version>1.1-groovy-2.4</spock-core.version>
+        <gmavenplus-plugin.version>1.6</gmavenplus-plugin.version>
+    </properties>
+</project>
+

core-groovy-collections/src/test/groovy/com/baeldung/map/MapTest.groovy

@@ -0,0 +1,148 @@
+package com.baeldung.map;
+
+import static groovy.test.GroovyAssert.*
+import org.junit.Test
+
+class MapTest{
+
+    @Test
+    void createMap() {
+
+        def emptyMap = [:]
+        assertNotNull(emptyMap)
+
+        assertTrue(emptyMap instanceof java.util.LinkedHashMap)
+
+        def map = [name:"Jerry", age: 42, city: "New York"]
+        assertTrue(map.size() == 3)
+    }
+
+    @Test
+    void addItemsToMap() {
+
+        def map = [name:"Jerry"]
+
+        map["age"] = 42
+
+        map.city = "New York"
+
+        def hobbyLiteral = "hobby"
+        def hobbyMap = [(hobbyLiteral): "Singing"]
+        map.putAll(hobbyMap)
+
+        assertTrue(map == [name:"Jerry", age: 42, city: "New York", hobby:"Singing"])
+        assertTrue(hobbyMap.hobby == "Singing")
+        assertTrue(hobbyMap[hobbyLiteral] == "Singing")
+        
+        map.plus([1:20]) // returns new map
+
+        map << [2:30]
+
+    }
+
+    @Test
+    void getItemsFromMap() {
+
+        def map = [name:"Jerry", age: 42, city: "New York", hobby:"Singing"]
+
+        assertTrue(map["name"] == "Jerry")
+
+        assertTrue(map.name == "Jerry")
+
+        def propertyAge = "age"
+        assertTrue(map[propertyAge] == 42)
+    }
+
+    @Test
+    void removeItemsFromMap() {
+
+        def map = [1:20, a:30, 2:42, 4:34, ba:67, 6:39, 7:49]
+
+        def minusMap = map.minus([2:42, 4:34]);
+        assertTrue(minusMap == [1:20, a:30, ba:67, 6:39, 7:49])
+
+        minusMap.removeAll{it -> it.key instanceof String}
+        assertTrue( minusMap == [ 1:20, 6:39, 7:49])
+
+        minusMap.retainAll{it -> it.value %2 == 0}
+        assertTrue( minusMap == [1:20])
+    }
+
+    @Test
+    void iteratingOnMaps(){
+        def map = [name:"Jerry", age: 42, city: "New York", hobby:"Singing"]
+
+        map.each{ entry -> println "$entry.key: $entry.value" }
+
+        map.eachWithIndex{ entry, i -> println "$i $entry.key: $entry.value" }
+
+        map.eachWithIndex{ key, value, i -> println "$i $key: $value" }
+    }
+
+    @Test
+    void filteringAndSearchingMaps(){
+        def map = [name:"Jerry", age: 42, city: "New York", hobby:"Singing"]
+
+        assertTrue(map.find{ it.value == "New York"}.key == "city")
+
+        assertTrue(map.findAll{ it.value == "New York"} == [city : "New York"])
+
+        map.grep{it.value == "New York"}.each{ it -> assertTrue(it.key == "city" && it.value == "New York")}
+
+        assertTrue(map.every{it -> it.value instanceof String} == false)
+
+        assertTrue(map.any{it -> it.value instanceof String} == true)
+    }
+
+    @Test
+    void collect(){
+
+        def map = [1: [name:"Jerry", age: 42, city: "New York"],
+            2: [name:"Long", age: 25, city: "New York"],
+            3: [name:"Dustin", age: 29, city: "New York"],
+            4: [name:"Dustin", age: 34, city: "New York"]]
+
+        def names = map.collect{entry -> entry.value.name} // returns only list
+        assertTrue(names == ["Jerry", "Long", "Dustin", "Dustin"])
+
+        def uniqueNames = map.collect([] as HashSet){entry -> entry.value.name}
+        assertTrue(uniqueNames == ["Jerry", "Long", "Dustin"] as Set)
+
+        def idNames = map.collectEntries{key, value -> [key, value.name]}
+        assertTrue(idNames == [1:"Jerry", 2: "Long", 3:"Dustin", 4: "Dustin"])
+
+        def below30Names = map.findAll{it.value.age < 30}.collect{key, value -> value.name}
+        assertTrue(below30Names == ["Long", "Dustin"])
+
+
+    }
+
+    @Test
+    void group(){
+        def map = [1:20, 2: 40, 3: 11, 4: 93]
+
+        def subMap = map.groupBy{it.value % 2}
+        println subMap
+        assertTrue(subMap == [0:[1:20, 2:40 ], 1:[3:11, 4:93]])
+
+        def keySubMap = map.subMap([1, 2])
+        assertTrue(keySubMap == [1:20, 2:40])
+
+    }
+
+    @Test
+    void sorting(){
+        def map = [ab:20, a: 40, cb: 11, ba: 93]
+
+        def naturallyOrderedMap = map.sort()
+        assertTrue([a:40, ab:20, ba:93, cb:11] == naturallyOrderedMap)
+
+        def compSortedMap = map.sort({ k1, k2 -> k1 <=> k2 } as Comparator)
+        assertTrue([a:40, ab:20, ba:93, cb:11] == compSortedMap)
+
+        def cloSortedMap = map.sort({ it1, it2 -> it1.value <=> it1.value })
+        assertTrue([cb:11, ab:20, a:40, ba:93] == cloSortedMap)
+
+    }
+
+}

core-groovy/README.md

@@ -8,4 +8,8 @@
 - [Types of Strings in Groovy](https://www.baeldung.com/groovy-strings)
 - [A Quick Guide to Iterating a Map in Groovy](https://www.baeldung.com/groovy-map-iterating)
 - [An Introduction to Traits in Groovy](https://www.baeldung.com/groovy-traits)
+- [Closures in Groovy](https://www.baeldung.com/groovy-closures)
+- [Finding Elements in Collections in Groovy](https://www.baeldung.com/groovy-collections-find-elements)
 - [Lists in Groovy](https://www.baeldung.com/groovy-lists)
+- [Converting a String to a Date in Groovy](https://www.baeldung.com/groovy-string-to-date)
+- [Guide to I/O in Groovy](https://www.baeldung.com/groovy-io)

core-groovy/src/main/groovy/com/baeldung/Person.groovy

@@ -0,0 +1,37 @@
+package com.baeldung
+
+class Person {
+    private String firstname
+    private String lastname
+    private Integer age
+
+    Person(String firstname, String lastname, Integer age) {
+        this.firstname = firstname
+        this.lastname = lastname
+        this.age = age
+    }
+
+    String getFirstname() {
+        return firstname
+    }
+
+    void setFirstname(String firstname) {
+        this.firstname = firstname
+    }
+
+    String getLastname() {
+        return lastname
+    }
+
+    void setLastname(String lastname) {
+        this.lastname = lastname
+    }
+
+    Integer getAge() {
+        return age
+    }
+
+    void setAge(Integer age) {
+        this.age = age
+    }
+}

core-groovy/src/main/groovy/com/baeldung/closures/Closures.groovy

@@ -0,0 +1,87 @@
+package com.baeldung.closures
+
+class Closures {
+    
+    def printWelcome = {
+        println "Welcome to Closures!"
+    }
+    
+    def print = { name ->
+        println name
+    }
+    
+    def formatToLowerCase(name) {
+        return name.toLowerCase()
+    }
+    def formatToLowerCaseClosure = { name ->
+        return name.toLowerCase()
+    }
+    
+    def count=0
+    
+    def increaseCount = {
+        count++
+    }
+    
+    def greet = {
+        return "Hello! ${it}"
+    }
+   
+    def multiply = { x, y ->
+        return x*y
+    }
+    
+    def calculate = {int x, int y, String operation ->
+        
+        //log closure
+        def log = {
+            println "Performing $it"
+        }
+        
+        def result = 0    
+        switch(operation) {
+            case "ADD":
+                log("Addition")
+                result = x+y
+                break
+            case "SUB":
+                log("Subtraction")
+                result = x-y
+                break
+            case "MUL":
+                log("Multiplication")
+                result = x*y
+                break
+            case "DIV":
+                log("Division")
+                result = x/y
+                break
+        }
+        return result
+    }
+    
+    def addAll = { int... args ->
+        return args.sum()
+    }
+    
+    def volume(Closure areaCalculator, int... dimensions) {
+        if(dimensions.size() == 3) {
+            
+            //consider dimension[0] = length, dimension[1] = breadth, dimension[2] = height
+            //for cube and cuboid
+            return areaCalculator(dimensions[0], dimensions[1]) * dimensions[2]
+        } else if(dimensions.size() == 2) {
+            
+            //consider dimension[0] = radius, dimension[1] = height
+            //for cylinder and cone
+            return areaCalculator(dimensions[0]) * dimensions[1]
+        } else if(dimensions.size() == 1) {
+            
+            //consider dimension[0] = radius
+            //for sphere
+            return areaCalculator(dimensions[0]) * dimensions[0]
+        }
+        
+    }
+     
+}

core-groovy/src/main/groovy/com/baeldung/closures/Employee.groovy

@@ -0,0 +1,6 @@
+package com.baeldung.closures
+
+class Employee {
+    
+    String fullName
+}

core-groovy/src/test/groovy/com/baeldung/closures/ClosuresUnitTest.groovy

@@ -0,0 +1,80 @@
+package com.baeldung.closures
+
+import spock.lang.Specification
+
+class ClosuresUnitTest extends GroovyTestCase {
+
+    Closures closures = new Closures()
+    
+    void testDeclaration() {
+        
+        closures.print("Hello! Closure")
+        closures.formatToLowerCaseClosure("Hello! Closure")
+        
+        closures.print.call("Hello! Closure")
+        closures.formatToLowerCaseClosure.call("Hello! Closure")
+        
+    }
+    
+    void testClosureVsMethods() {   
+        assert closures.formatToLowerCase("TONY STARK") == closures.formatToLowerCaseClosure("Tony STark")
+    }
+    
+    void testParameters() {
+        //implicit parameter
+        assert closures.greet("Alex") == "Hello! Alex"
+        
+        //multiple parameters
+        assert closures.multiply(2, 4) == 8
+        
+        assert closures.calculate(12, 4, "ADD") == 16
+        assert closures.calculate(12, 4, "SUB") == 8
+        assert closures.calculate(43, 8, "DIV") == 5.375
+                
+        //varags
+        assert closures.addAll(12, 10, 14) == 36
+       
+    }
+    
+    void testClosureAsAnArgument() {
+        assert closures.volume({ l, b -> return l*b }, 12, 6, 10) == 720
+        
+        assert closures.volume({ radius -> return Math.PI*radius*radius/3 }, 5, 10) == Math.PI * 250/3
+    }
+    
+    void testGStringsLazyEvaluation() {
+        def name = "Samwell"
+        def welcomeMsg = "Welcome! $name"
+        
+        assert welcomeMsg == "Welcome! Samwell"
+        
+        // changing the name does not affect original interpolated value
+        name = "Tarly"
+        assert welcomeMsg != "Welcome! Tarly"
+        
+        def fullName = "Tarly Samson"
+        def greetStr = "Hello! ${-> fullName}"
+        
+        assert greetStr == "Hello! Tarly Samson"
+
+        // this time changing the variable affects the interpolated String's value
+        fullName = "Jon Smith"
+        assert greetStr == "Hello! Jon Smith"
+    }
+    
+    void testClosureInLists() {
+        def list = [10, 11, 12, 13, 14, true, false, "BUNTHER"]
+        list.each {
+            println it
+        }
+        
+        assert [13, 14] == list.findAll{ it instanceof Integer && it >= 13}
+    }
+    
+    void testClosureInMaps() {
+        def map = [1:10, 2:30, 4:5]
+        
+        assert [10, 60, 20] == map.collect{it.key * it.value}
+    }
+    
+}

core-groovy/src/test/groovy/com/baeldung/lists/ListTest.groovy

@@ -129,13 +129,13 @@ class ListTest{
         assertTrue(filterList.findAll{it > 3} == [4, 5, 6, 76])
 
         assertTrue(filterList.findAll{ it instanceof Number} == [2, 1, 3, 4, 5, 6, 76])
-        
+
         assertTrue(filterList.grep( Number )== [2, 1, 3, 4, 5, 6, 76])
-        
+
         assertTrue(filterList.grep{ it> 6 }== [76])
 
         def conditionList = [2, 1, 3, 4, 5, 6, 76]
-        
+
         assertFalse(conditionList.every{ it < 6})
 
         assertTrue(conditionList.any{ it%2 == 0})
@@ -165,7 +165,7 @@ class ListTest{
 
         def strList = ["na", "ppp", "as"]
         assertTrue(strList.max() == "ppp")
-        
+
         Comparator minc = {a,b -> a == b? 0: a < b? -1 : 1}
         def numberList = [3, 2, 0, 7]
         assertTrue(numberList.min(minc) == 0)

core-groovy/src/test/groovy/com/baeldung/lists/ListUnitTest.groovy

@@ -0,0 +1,58 @@
+package com.baeldung.lists
+
+import com.baeldung.Person
+import org.junit.Test
+
+import static org.junit.Assert.*
+
+class ListUnitTest {
+
+    private final personList = [
+      new Person("Regina", "Fitzpatrick", 25),
+      new Person("Abagail", "Ballard", 26),
+      new Person("Lucian", "Walter", 30),
+    ]
+
+    @Test
+    void whenListContainsElement_thenCheckReturnsTrue() {
+        def list = ['a', 'b', 'c']
+
+        assertTrue(list.indexOf('a') > -1)
+        assertTrue(list.contains('a'))
+    }
+
+    @Test
+    void whenListContainsElement_thenCheckWithMembershipOperatorReturnsTrue() {
+        def list = ['a', 'b', 'c']
+
+        assertTrue('a' in list)
+    }
+
+    @Test
+    void givenListOfPerson_whenUsingStreamMatching_thenShouldEvaluateList() {
+        assertTrue(personList.stream().anyMatch {it.age > 20})
+        assertFalse(personList.stream().allMatch {it.age < 30})
+    }
+
+    @Test
+    void givenListOfPerson_whenUsingCollectionMatching_thenShouldEvaluateList() {
+        assertTrue(personList.any {it.age > 20})
+        assertFalse(personList.every {it.age < 30})
+    }
+
+    @Test
+    void givenListOfPerson_whenUsingStreamFind_thenShouldReturnMatchingElements() {
+        assertTrue(personList.stream().filter {it.age > 20}.findAny().isPresent())
+        assertFalse(personList.stream().filter {it.age > 30}.findAny().isPresent())
+        assertTrue(personList.stream().filter {it.age > 20}.findAll().size() == 3)
+        assertTrue(personList.stream().filter {it.age > 30}.findAll().isEmpty())
+    }
+
+    @Test
+    void givenListOfPerson_whenUsingCollectionFind_thenShouldReturnMatchingElements() {
+        assertNotNull(personList.find {it.age > 20})
+        assertNull(personList.find {it.age > 30})
+        assertTrue(personList.findAll {it.age > 20}.size() == 3)
+        assertTrue(personList.findAll {it.age > 30}.isEmpty())
+    }
+}

core-groovy/src/test/groovy/com/baeldung/map/MapTest.groovy

@@ -0,0 +1,148 @@
+package com.baeldung.groovy.map;
+
+import static groovy.test.GroovyAssert.*
+import org.junit.Test
+
+class MapTest{
+
+    @Test
+    void createMap() {
+
+        def emptyMap = [:]
+        assertNotNull(emptyMap)
+
+        assertTrue(emptyMap instanceof java.util.LinkedHashMap)
+
+        def map = [name:"Jerry", age: 42, city: "New York"]
+        assertTrue(map.size() == 3)
+    }
+
+    @Test
+    void addItemsToMap() {
+
+        def map = [name:"Jerry"]
+
+        map["age"] = 42
+
+        map.city = "New York"
+
+        def hobbyLiteral = "hobby"
+        def hobbyMap = [(hobbyLiteral): "Singing"]
+        map.putAll(hobbyMap)
+
+        assertTrue(map == [name:"Jerry", age: 42, city: "New York", hobby:"Singing"])
+        assertTrue(hobbyMap.hobby == "Singing")
+        assertTrue(hobbyMap[hobbyLiteral] == "Singing")
+        
+        map.plus([1:20]) // returns new map
+
+        map << [2:30]
+
+    }
+
+    @Test
+    void getItemsFromMap() {
+
+        def map = [name:"Jerry", age: 42, city: "New York", hobby:"Singing"]
+
+        assertTrue(map["name"] == "Jerry")
+
+        assertTrue(map.name == "Jerry")
+
+        def propertyAge = "age"
+        assertTrue(map[propertyAge] == 42)
+    }
+
+    @Test
+    void removeItemsFromMap() {
+
+        def map = [1:20, a:30, 2:42, 4:34, ba:67, 6:39, 7:49]
+
+        def minusMap = map.minus([2:42, 4:34]);
+        assertTrue(minusMap == [1:20, a:30, ba:67, 6:39, 7:49])
+
+        minusMap.removeAll{it -> it.key instanceof String}
+        assertTrue( minusMap == [ 1:20, 6:39, 7:49])
+
+        minusMap.retainAll{it -> it.value %2 == 0}
+        assertTrue( minusMap == [1:20])
+    }
+
+    @Test
+    void iteratingOnMaps(){
+        def map = [name:"Jerry", age: 42, city: "New York", hobby:"Singing"]
+
+        map.each{ entry -> println "$entry.key: $entry.value" }
+
+        map.eachWithIndex{ entry, i -> println "$i $entry.key: $entry.value" }
+
+        map.eachWithIndex{ key, value, i -> println "$i $key: $value" }
+    }
+
+    @Test
+    void filteringAndSearchingMaps(){
+        def map = [name:"Jerry", age: 42, city: "New York", hobby:"Singing"]
+
+        assertTrue(map.find{ it.value == "New York"}.key == "city")
+
+        assertTrue(map.findAll{ it.value == "New York"} == [city : "New York"])
+
+        map.grep{it.value == "New York"}.each{ it -> assertTrue(it.key == "city" && it.value == "New York")}
+
+        assertTrue(map.every{it -> it.value instanceof String} == false)
+
+        assertTrue(map.any{it -> it.value instanceof String} == true)
+    }
+
+    @Test
+    void collect(){
+
+        def map = [1: [name:"Jerry", age: 42, city: "New York"],
+            2: [name:"Long", age: 25, city: "New York"],
+            3: [name:"Dustin", age: 29, city: "New York"],
+            4: [name:"Dustin", age: 34, city: "New York"]]
+
+        def names = map.collect{entry -> entry.value.name} // returns only list
+        assertTrue(names == ["Jerry", "Long", "Dustin", "Dustin"])
+
+        def uniqueNames = map.collect([] as HashSet){entry -> entry.value.name}
+        assertTrue(uniqueNames == ["Jerry", "Long", "Dustin"] as Set)
+
+        def idNames = map.collectEntries{key, value -> [key, value.name]}
+        assertTrue(idNames == [1:"Jerry", 2: "Long", 3:"Dustin", 4: "Dustin"])
+
+        def below30Names = map.findAll{it.value.age < 30}.collect{key, value -> value.name}
+        assertTrue(below30Names == ["Long", "Dustin"])
+
+
+    }
+
+    @Test
+    void group(){
+        def map = [1:20, 2: 40, 3: 11, 4: 93]
+
+        def subMap = map.groupBy{it.value % 2}
+        println subMap
+        assertTrue(subMap == [0:[1:20, 2:40 ], 1:[3:11, 4:93]])
+
+        def keySubMap = map.subMap([1, 2])
+        assertTrue(keySubMap == [1:20, 2:40])
+
+    }
+
+    @Test
+    void sorting(){
+        def map = [ab:20, a: 40, cb: 11, ba: 93]
+
+        def naturallyOrderedMap = map.sort()
+        assertTrue([a:40, ab:20, ba:93, cb:11] == naturallyOrderedMap)
+
+        def compSortedMap = map.sort({ k1, k2 -> k1 <=> k2 } as Comparator)
+        assertTrue([a:40, ab:20, ba:93, cb:11] == compSortedMap)
+
+        def cloSortedMap = map.sort({ it1, it2 -> it1.value <=> it1.value })
+        assertTrue([cb:11, ab:20, a:40, ba:93] == cloSortedMap)
+
+    }
+
+}

core-groovy/src/test/groovy/com/baeldung/map/MapUnitTest.groovy

@@ -1,10 +1,18 @@
 package com.baeldung.map
 
-import static org.junit.Assert.*
+import com.baeldung.Person
 import org.junit.Test
 
+import static org.junit.Assert.*
+
 class MapUnitTest {
 
+    private final personMap = [
+      Regina : new Person("Regina", "Fitzpatrick", 25),
+      Abagail: new Person("Abagail", "Ballard", 26),
+      Lucian : new Person("Lucian", "Walter", 30)
+    ]
+
     @Test
     void whenUsingEach_thenMapIsIterated() {
         def map = [
@@ -63,7 +71,7 @@ class MapUnitTest {
             'FF6347' : 'Tomato',
             'FF4500' : 'Orange Red'
         ]
-        
+
         map.eachWithIndex { key, val, index ->
             def indent = ((index == 0 || index % 2 == 0) ? "   " : "")
             println "$indent Hex Code: $key = Color Name: $val"
@@ -82,4 +90,65 @@ class MapUnitTest {
             println "Hex Code: $entry.key = Color Name: $entry.value"
         }
     }
+
+    @Test
+    void whenMapContainsKeyElement_thenCheckReturnsTrue() {
+        def map = [a: 'd', b: 'e', c: 'f']
+
+        assertTrue(map.containsKey('a'))
+        assertFalse(map.containsKey('e'))
+        assertTrue(map.containsValue('e'))
+    }
+
+    @Test
+    void whenMapContainsKeyElement_thenCheckByMembershipReturnsTrue() {
+        def map = [a: 'd', b: 'e', c: 'f']
+
+        assertTrue('a' in map)
+        assertFalse('f' in map)
+    }
+
+    @Test
+    void whenMapContainsFalseBooleanValues_thenCheckReturnsFalse() {
+        def map = [a: true, b: false, c: null]
+
+        assertTrue(map.containsKey('b'))
+        assertTrue('a' in map)
+        assertFalse('b' in map)
+        assertFalse('c' in map)
+    }
+
+    @Test
+    void givenMapOfPerson_whenUsingStreamMatching_thenShouldEvaluateMap() {
+        assertTrue(personMap.keySet().stream().anyMatch {it == "Regina"})
+        assertFalse(personMap.keySet().stream().allMatch {it == "Albert"})
+        assertFalse(personMap.values().stream().allMatch {it.age < 30})
+        assertTrue(personMap.entrySet().stream().anyMatch {it.key == "Abagail" && it.value.lastname == "Ballard"})
+    }
+
+    @Test
+    void givenMapOfPerson_whenUsingCollectionMatching_thenShouldEvaluateMap() {
+        assertTrue(personMap.keySet().any {it == "Regina"})
+        assertFalse(personMap.keySet().every {it == "Albert"})
+        assertFalse(personMap.values().every {it.age < 30})
+        assertTrue(personMap.any {firstname, person -> firstname == "Abagail" && person.lastname == "Ballard"})
+    }
+
+    @Test
+    void givenMapOfPerson_whenUsingCollectionFind_thenShouldReturnElements() {
+        assertNotNull(personMap.find {it.key == "Abagail" && it.value.lastname == "Ballard"})
+        assertTrue(personMap.findAll {it.value.age > 20}.size() == 3)
+    }
+
+    @Test
+    void givenMapOfPerson_whenUsingStreamFind_thenShouldReturnElements() {
+        assertTrue(
+          personMap.entrySet().stream()
+            .filter {it.key == "Abagail" && it.value.lastname == "Ballard"}
+            .findAny().isPresent())
+        assertTrue(
+          personMap.entrySet().stream()
+            .filter {it.value.age > 20}
+            .findAll().size() == 3)
+    }
 }

core-groovy/src/test/groovy/com/baeldung/set/SetUnitTest.groovy

@@ -0,0 +1,16 @@
+package com.baeldung.set
+
+import org.junit.Test
+
+import static org.junit.Assert.assertTrue
+
+class SetUnitTest {
+
+    @Test
+    void whenSetContainsElement_thenCheckReturnsTrue() {
+        def set = ['a', 'b', 'c'] as Set
+
+        assertTrue(set.contains('a'))
+        assertTrue('a' in set)
+    }
+}

core-groovy/src/test/groovy/com/baeldung/strings/StringMatchingSpec.groovy

@@ -0,0 +1,44 @@
+package com.baeldung.strings
+
+import spock.lang.Specification
+
+import java.util.regex.Pattern
+
+class StringMatchingSpec extends Specification {
+
+    def "pattern operator example"() {
+        given: "a pattern"
+        def p = ~'foo'
+
+        expect:
+        p instanceof Pattern
+
+        and: "you can use slash strings to avoid escaping of blackslash"
+        def digitPattern = ~/\d*/
+        digitPattern.matcher('4711').matches()
+    }
+
+    def "match operator example"() {
+        expect:
+        'foobar' ==~ /.*oba.*/
+
+        and: "matching is strict"
+        !('foobar' ==~ /foo/)
+    }
+
+    def "find operator example"() {
+        when: "using the find operator"
+        def matcher = 'foo and bar, baz and buz' =~ /(\w+) and (\w+)/
+
+        then: "will find groups"
+        matcher.size() == 2
+
+        and: "can access groups using array"
+        matcher[0][0] == 'foo and bar'
+        matcher[1][2] == 'buz'
+
+        and: "you can use it as a predicate"
+        'foobarbaz' =~ /bar/
+    }
+
+}

core-java-11/README.md

@@ -4,3 +4,6 @@
 - [Java 11 Local Variable Syntax for Lambda Parameters](https://www.baeldung.com/java-var-lambda-params)
 - [Java 11 String API Additions](https://www.baeldung.com/java-11-string-api)
 - [Java 11 Nest Based Access Control](https://www.baeldung.com/java-nest-based-access-control)
+- [Exploring the New HTTP Client in Java 9 and 11](https://www.baeldung.com/java-9-http-client)
+- [An Introduction to Epsilon GC: A No-Op Experimental Garbage Collector](https://www.baeldung.com/jvm-epsilon-gc-garbage-collector)
+- [Guide to jlink](https://www.baeldung.com/jlink)

core-java-11/pom.xml

@@ -14,6 +14,14 @@
         <version>1.0.0-SNAPSHOT</version>
     </parent>
 
+    <dependencies>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+        </dependency>
+    </dependencies>
+
     <build>
         <plugins>
             <plugin>
@@ -31,6 +39,7 @@
     <properties>
         <maven.compiler.source.version>11</maven.compiler.source.version>
         <maven.compiler.target.version>11</maven.compiler.target.version>
+        <guava.version>27.1-jre</guava.version>
     </properties>
 
 </project>

core-java-11/src/modules/jlinkModule/com/baeldung/jlink/HelloWorld.java

@@ -0,0 +1,12 @@
+package com.baeldung.jlink;
+
+import java.util.logging.Logger;
+
+public class HelloWorld {
+
+    private static final Logger LOG = Logger.getLogger(HelloWorld.class.getName());
+
+    public static void main(String[] args) {
+        LOG.info("Hello World!");
+    }
+}

core-java-11/src/modules/jlinkModule/module-info.java

@@ -0,0 +1,3 @@
+module jlinkModule {
+    requires java.logging;
+}

core-java-11/src/test/java/com/baeldung/EmptyStringToEmptyOptionalUnitTest.java

@@ -0,0 +1,32 @@
+package com.baeldung;
+
+import com.google.common.base.Strings;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.Optional;
+import java.util.function.Predicate;
+
+public class EmptyStringToEmptyOptionalUnitTest {
+
+    @Test
+    public void givenEmptyString_whenFilteringOnOptional_thenEmptyOptionalIsReturned() {
+        String str = "";
+        Optional<String> opt = Optional.ofNullable(str).filter(s -> !s.isEmpty());
+        Assert.assertFalse(opt.isPresent());
+    }
+
+    @Test
+    public void givenEmptyString_whenFilteringOnOptionalInJava11_thenEmptyOptionalIsReturned() {
+        String str = "";
+        Optional<String> opt = Optional.ofNullable(str).filter(Predicate.not(String::isEmpty));
+        Assert.assertFalse(opt.isPresent());
+    }
+
+    @Test
+    public void givenEmptyString_whenPassingResultOfEmptyToNullToOfNullable_thenEmptyOptionalIsReturned() {
+        String str = "";
+        Optional<String> opt = Optional.ofNullable(Strings.emptyToNull(str));
+        Assert.assertFalse(opt.isPresent());
+    }
+}

core-java-12/pom.xml

@@ -0,0 +1,49 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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>
+    <groupId>com.baeldung</groupId>
+    <artifactId>core-java-12</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-12</name>
+    <packaging>jar</packaging>
+    <url>http://maven.apache.org</url>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source.version}</source>
+                    <target>${maven.compiler.target.version}</target>
+                    <compilerArgs>--enable-preview</compilerArgs>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <maven.compiler.source.version>12</maven.compiler.source.version>
+        <maven.compiler.target.version>12</maven.compiler.target.version>
+        <assertj.version>3.6.1</assertj.version>
+    </properties>
+
+</project>

core-java-12/src/test/java/com/baeldung/collectors/CollectorsUnitTest.java

@@ -0,0 +1,71 @@
+package com.baeldung.collectors;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+
+import org.junit.Test;
+
+import static java.util.stream.Collectors.maxBy;
+import static java.util.stream.Collectors.minBy;
+import static java.util.stream.Collectors.teeing;
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Unit tests for collectors additions in Java 12.
+ */
+public class CollectorsUnitTest {
+
+    @Test
+    public void whenTeeing_ItShouldCombineTheResultsAsExpected() {
+        List<Integer> numbers = Arrays.asList(42, 4, 2, 24);
+        Range range = numbers.stream()
+            .collect(teeing(minBy(Integer::compareTo), maxBy(Integer::compareTo), (min, max) -> new Range(min.orElse(null), max.orElse(null))));
+
+        assertThat(range).isEqualTo(new Range(2, 42));
+    }
+
+    /**
+     * Represents a closed range of numbers between {@link #min} and
+     * {@link #max}, both inclusive.
+     */
+    private static class Range {
+
+        private final Integer min;
+
+        private final Integer max;
+
+        Range(Integer min, Integer max) {
+            this.min = min;
+            this.max = max;
+        }
+
+        Integer getMin() {
+            return min;
+        }
+
+        Integer getMax() {
+            return max;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o)
+                return true;
+            if (o == null || getClass() != o.getClass())
+                return false;
+            Range range = (Range) o;
+            return Objects.equals(getMin(), range.getMin()) && Objects.equals(getMax(), range.getMax());
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(getMin(), getMax());
+        }
+
+        @Override
+        public String toString() {
+            return "Range{" + "min=" + min + ", max=" + max + '}';
+        }
+    }
+}

core-java-12/src/test/java/com/baeldung/switchExpression/SwitchUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.switchExpression;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class SwitchUnitTest {
+
+    @Test
+    public void switchJava12(){
+
+        var month = Month.AUG;
+
+        var value = switch(month){
+            case JAN,JUN, JUL -> 3;
+            case FEB,SEP, OCT, NOV, DEC -> 1;
+            case MAR,MAY, APR, AUG -> 2;
+        };
+
+        Assert.assertEquals(value, 2);
+    }
+
+    @Test
+    public void switchLocalVariable(){
+        var month = Month.AUG;
+        int i = switch (month){
+            case JAN,JUN, JUL -> 3;
+            case FEB,SEP, OCT, NOV, DEC -> 1;
+            case MAR,MAY, APR, AUG -> {
+                int j = month.toString().length() * 4;
+                break j;
+            }
+        };
+        Assert.assertEquals(12, i);
+    }
+
+    enum Month {JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC}
+}

core-java-8-2/README.md

@@ -0,0 +1,6 @@
+=========
+
+## Core Java 8 Cookbooks and Examples (part 2)
+
+### Relevant Articles: 
+- [Anonymous Classes in Java](http://www.baeldung.com/)

core-java-8-2/pom.xml

@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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>
+    <groupId>com.baeldung</groupId>
+    <artifactId>core-java-8-2</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-8-2</name>
+    <packaging>jar</packaging>
+
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../parent-java</relativePath>
+    </parent>
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+    </properties>
+
+    <dependencies>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+
+    </build>
+</project>

core-java-8/README.md

@@ -3,7 +3,7 @@
 ## Core Java 8 Cookbooks and Examples
 
 ### Relevant Articles: 
-- [Java 8 Collectors](http://www.baeldung.com/java-8-collectors)
+- [Guide to Java 8’s Collectors](http://www.baeldung.com/java-8-collectors)
 - [Functional Interfaces in Java 8](http://www.baeldung.com/java-8-functional-interfaces)
 - [Java 8 – Powerful Comparison with Lambdas](http://www.baeldung.com/java-8-sort-lambda)
 - [New Features in Java 8](http://www.baeldung.com/java-8-new-features)

core-java-8/src/main/java/com/baeldung/Adder.java

@@ -1,12 +0,0 @@
-package com.baeldung;
-
-import java.util.function.Consumer;
-import java.util.function.Function;
-
-public interface Adder {
-
-    String addWithFunction(Function<String, String> f);
-
-    void addWithConsumer(Consumer<Integer> f);
-
-}

core-java-8/src/main/java/com/baeldung/AdderImpl.java

@@ -1,18 +0,0 @@
-package com.baeldung;
-
-
-import java.util.function.Consumer;
-import java.util.function.Function;
-
-public class AdderImpl implements Adder {
-
-    @Override
-    public String addWithFunction(final Function<String, String> f) {
-        return f.apply("Something ");
-    }
-
-    @Override
-    public void addWithConsumer(final Consumer<Integer> f) {
-    }
-
-}

core-java-8/src/main/java/com/baeldung/java8/lambda/tips/Bar.java

@@ -1,4 +1,4 @@
-package com.baeldung;
+package com.baeldung.java8.lambda.tips;
 
 
 @FunctionalInterface

core-java-8/src/main/java/com/baeldung/java8/lambda/tips/Baz.java

@@ -1,4 +1,4 @@
-package com.baeldung;
+package com.baeldung.java8.lambda.tips;
 
 
 @FunctionalInterface

core-java-8/src/main/java/com/baeldung/java8/lambda/tips/Foo.java

@@ -1,4 +1,4 @@
-package com.baeldung;
+package com.baeldung.java8.lambda.tips;
 
 
 @FunctionalInterface

core-java-8/src/main/java/com/baeldung/java8/lambda/tips/FooExtended.java

@@ -1,4 +1,4 @@
-package com.baeldung;
+package com.baeldung.java8.lambda.tips;
 
 
 @FunctionalInterface

core-java-8/src/main/java/com/baeldung/java8/lambda/tips/Processor.java

@@ -0,0 +1,12 @@
+package com.baeldung.java8.lambda.tips;
+
+import java.util.concurrent.Callable;
+import java.util.function.Supplier;
+
+public interface Processor {
+
+    String processWithCallable(Callable<String> c) throws Exception;
+
+    String processWithSupplier(Supplier<String> s);
+
+}

core-java-8/src/main/java/com/baeldung/java8/lambda/tips/ProcessorImpl.java

@@ -0,0 +1,20 @@
+package com.baeldung.java8.lambda.tips;
+
+
+import java.util.concurrent.Callable;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+public class ProcessorImpl implements Processor {
+
+    @Override
+    public String processWithCallable(Callable<String> c) throws Exception {
+        return c.call();
+    }
+
+    @Override
+    public String processWithSupplier(Supplier<String> s) {
+        return s.get();
+    }
+}

core-java-8/src/main/java/com/baeldung/java8/lambda/tips/UseFoo.java

@@ -1,4 +1,4 @@
-package com.baeldung;
+package com.baeldung.java8.lambda.tips;
 
 
 import java.util.function.Function;

core-java-8/src/test/java/com/baeldung/java8/Java8SortUnitTest.java

@@ -124,11 +124,44 @@ public class Java8SortUnitTest {
 
     @Test
     public final void givenStreamCustomOrdering_whenSortingEntitiesByName_thenCorrectlySorted() {
-        
         final List<Human> humans = Lists.newArrayList(new Human("Sarah", 10), new Human("Jack", 12));
         final Comparator<Human> nameComparator = (h1, h2) -> h1.getName().compareTo(h2.getName());
         
         final List<Human> sortedHumans = humans.stream().sorted(nameComparator).collect(Collectors.toList());
         Assert.assertThat(sortedHumans.get(0), equalTo(new Human("Jack", 12)));
     }
+
+    @Test
+    public final void givenStreamComparatorOrdering_whenSortingEntitiesByName_thenCorrectlySorted() {
+        final List<Human> humans = Lists.newArrayList(new Human("Sarah", 10), new Human("Jack", 12));
+
+        final List<Human> sortedHumans = humans.stream().sorted(Comparator.comparing(Human::getName)).collect(Collectors.toList());
+        Assert.assertThat(sortedHumans.get(0), equalTo(new Human("Jack", 12)));
+    }
+
+    @Test
+    public final void givenStreamNaturalOrdering_whenSortingEntitiesByNameReversed_thenCorrectlySorted() {
+        final List<String> letters = Lists.newArrayList("B", "A", "C");
+
+        final List<String> reverseSortedLetters = letters.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());
+        Assert.assertThat(reverseSortedLetters.get(0), equalTo("C"));
+    }
+
+    @Test
+    public final void givenStreamCustomOrdering_whenSortingEntitiesByNameReversed_thenCorrectlySorted() {
+        final List<Human> humans = Lists.newArrayList(new Human("Sarah", 10), new Human("Jack", 12));
+        final Comparator<Human> reverseNameComparator = (h1, h2) -> h2.getName().compareTo(h1.getName());
+
+        final List<Human> reverseSortedHumans = humans.stream().sorted(reverseNameComparator).collect(Collectors.toList());
+        Assert.assertThat(reverseSortedHumans.get(0), equalTo(new Human("Sarah", 10)));
+    }
+
+    @Test
+    public final void givenStreamComparatorOrdering_whenSortingEntitiesByNameReversed_thenCorrectlySorted() {
+        final List<Human> humans = Lists.newArrayList(new Human("Sarah", 10), new Human("Jack", 12));
+
+        final List<Human> reverseSortedHumans = humans.stream().sorted(Comparator.comparing(Human::getName, Comparator.reverseOrder())).collect(Collectors.toList());
+        Assert.assertThat(reverseSortedHumans.get(0), equalTo(new Human("Sarah", 10)));
+    }
+
 }

core-java-8/src/test/java/com/baeldung/java8/lambda/tips/Java8FunctionalInteracesLambdasUnitTest.java

@@ -1,8 +1,8 @@
-package com.baeldung.java8;
+package com.baeldung.java8.lambda.tips;
 
-import com.baeldung.Foo;
-import com.baeldung.FooExtended;
-import com.baeldung.UseFoo;
+import com.baeldung.java8.lambda.tips.Foo;
+import com.baeldung.java8.lambda.tips.FooExtended;
+import com.baeldung.java8.lambda.tips.UseFoo;
 import org.junit.Before;
 import org.junit.Test;
 

core-java-8/src/test/java/com/baeldung/java8/optional/OptionalUnitTest.java

@@ -27,34 +27,35 @@ public class OptionalUnitTest {
     @Test
     public void givenNonNull_whenCreatesNonNullable_thenCorrect() {
         String name = "baeldung";
-        Optional.of(name);
+        Optional<String> opt = Optional.of(name);
+        assertTrue(opt.isPresent());
     }
 
     @Test(expected = NullPointerException.class)
     public void givenNull_whenThrowsErrorOnCreate_thenCorrect() {
         String name = null;
-        Optional<String> opt = Optional.of(name);
+        Optional.of(name);
     }
 
     @Test
     public void givenNonNull_whenCreatesOptional_thenCorrect() {
         String name = "baeldung";
         Optional<String> opt = Optional.of(name);
-        assertEquals("Optional[baeldung]", opt.toString());
+        assertTrue(opt.isPresent());
     }
 
     @Test
     public void givenNonNull_whenCreatesNullable_thenCorrect() {
         String name = "baeldung";
         Optional<String> opt = Optional.ofNullable(name);
-        assertEquals("Optional[baeldung]", opt.toString());
+        assertTrue(opt.isPresent());
     }
 
     @Test
     public void givenNull_whenCreatesNullable_thenCorrect() {
         String name = null;
         Optional<String> opt = Optional.ofNullable(name);
-        assertEquals("Optional.empty", opt.toString());
+        assertFalse(opt.isPresent());
     }
     // Checking Value With isPresent()
 

core-java-8/src/test/java/com/baeldung/reduceIfelse/CalculatorUnitTest.java

@@ -29,4 +29,11 @@ public class CalculatorUnitTest {
         int result = calculator.calculate(new AddCommand(3, 7));
         assertEquals(10, result);
     }
+
+    @Test
+    public void whenCalculateUsingFactory_thenReturnCorrectResult() {
+        Calculator calculator = new Calculator();
+        int result = calculator.calculateUsingFactory(3, 4, "add");
+        assertEquals(7, result);
+    }
 }

core-java-9/README.md

@@ -5,27 +5,21 @@
 [Java 9 New Features](http://www.baeldung.com/new-java-9)
 
 ### Relevant Articles:
-- [Java 9 Stream API Improvements](http://www.baeldung.com/java-9-stream-api)
-- [Java 9 Convenience Factory Methods for Collections](http://www.baeldung.com/java-9-collections-factory-methods) 
+
+- [Java 9 New Features](https://www.baeldung.com/new-java-9)
 - [New Stream Collectors in Java 9](http://www.baeldung.com/java9-stream-collectors)
-- [Java 9 CompletableFuture API Improvements](http://www.baeldung.com/java-9-completablefuture)
-- [Java 9 Process API Improvements](http://www.baeldung.com/java-9-process-api)
-- [Introduction to Java 9 StackWalking API](http://www.baeldung.com/java-9-stackwalking-api)
 - [Introduction to Project Jigsaw](http://www.baeldung.com/project-jigsaw-java-modularity)
-- [Java 9 Optional API Additions](http://www.baeldung.com/java-9-optional)
-- [Java 9 Reactive Streams](http://www.baeldung.com/java-9-reactive-streams)
-- [Java 9 java.util.Objects Additions](http://www.baeldung.com/java-9-objects-new)
-- [Java 9 Variable Handles Demistyfied](http://www.baeldung.com/java-variable-handles)
+- [Java 9 Variable Handles Demystified](http://www.baeldung.com/java-variable-handles)
 - [Exploring the New HTTP Client in Java 9 and 11](http://www.baeldung.com/java-9-http-client)
 - [Method Handles in Java](http://www.baeldung.com/java-method-handles)
 - [Introduction to Chronicle Queue](http://www.baeldung.com/java-chronicle-queue)
-- [A Guide to Java 9 Modularity](http://www.baeldung.com/java-9-modularity)
 - [Optional orElse Optional](http://www.baeldung.com/java-optional-or-else-optional)
-- [Java 9 java.lang.Module API](http://www.baeldung.com/java-9-module-api)
 - [Iterate Through a Range of Dates in Java](https://www.baeldung.com/java-iterate-date-range)
 - [Initialize a HashMap in Java](https://www.baeldung.com/java-initialize-hashmap)
-- [Java 9 Platform Logging API](https://www.baeldung.com/java-9-logging-api)
-- [Guide to java.lang.Process API](https://www.baeldung.com/java-process-api)
 - [Immutable Set in Java](https://www.baeldung.com/java-immutable-set)
 - [Multi-Release Jar Files](https://www.baeldung.com/java-multi-release-jar)
 - [Ahead of Time Compilation (AoT)](https://www.baeldung.com/ahead-of-time-compilation)
+- [Java 9 Process API Improvements](https://www.baeldung.com/java-9-process-api)
+- [Guide to java.lang.Process API](https://www.baeldung.com/java-process-api)
+
+

core-java-arrays/src/main/java/com/baeldung/array/AddElementToEndOfArray.java

@@ -0,0 +1,34 @@
+package com.baeldung.array;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+
+public class AddElementToEndOfArray {
+
+    public Integer[] addElementUsingArraysCopyOf(Integer[] srcArray, int elementToAdd) {
+        Integer[] destArray = Arrays.copyOf(srcArray, srcArray.length + 1);
+
+        destArray[destArray.length - 1] = elementToAdd;
+        return destArray;
+    }
+
+    public Integer[] addElementUsingArrayList(Integer[] srcArray, int elementToAdd) {
+        Integer[] destArray = new Integer[srcArray.length + 1];
+
+        ArrayList<Integer> arrayList = new ArrayList<>(Arrays.asList(srcArray));
+        arrayList.add(elementToAdd);
+
+        return arrayList.toArray(destArray);
+    }
+
+    public Integer[] addElementUsingSystemArrayCopy(Integer[] srcArray, int elementToAdd) {
+        Integer[] destArray = new Integer[srcArray.length + 1];
+
+        System.arraycopy(srcArray, 0, destArray, 0, srcArray.length);
+
+        destArray[destArray.length - 1] = elementToAdd;
+
+        return destArray;
+    }
+
+}

core-java-arrays/src/test/java/com/baeldung/array/AddElementToEndOfArrayUnitTest.java

@@ -0,0 +1,49 @@
+package com.baeldung.array;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertArrayEquals;
+
+public class AddElementToEndOfArrayUnitTest {
+
+    AddElementToEndOfArray addElementToEndOfArray;
+
+    @Before
+    public void init() {
+        addElementToEndOfArray = new AddElementToEndOfArray();
+    }
+
+    @Test
+    public void givenSourceArrayAndElement_whenAddElementUsingArraysCopyIsInvoked_thenNewElementMustBeAdded() {
+        Integer[] sourceArray = {1, 2, 3, 4};
+        int elementToAdd = 5;
+
+        Integer[] destArray = addElementToEndOfArray.addElementUsingArraysCopyOf(sourceArray, elementToAdd);
+
+        Integer[] expectedArray = {1, 2, 3, 4, 5};
+        assertArrayEquals(expectedArray, destArray);
+    }
+
+    @Test
+    public void givenSourceArrayAndElement_whenAddElementUsingArrayListIsInvoked_thenNewElementMustBeAdded() {
+        Integer[] sourceArray = {1, 2, 3, 4};
+        int elementToAdd = 5;
+
+        Integer[] destArray = addElementToEndOfArray.addElementUsingArrayList(sourceArray, elementToAdd);
+
+        Integer[] expectedArray = {1, 2, 3, 4, 5};
+        assertArrayEquals(expectedArray, destArray);
+    }
+
+    @Test
+    public void givenSourceArrayAndElement_whenAddElementUsingSystemArrayCopyIsInvoked_thenNewElementMustBeAdded() {
+        Integer[] sourceArray = {1, 2, 3, 4};
+        int elementToAdd = 5;
+
+        Integer[] destArray = addElementToEndOfArray.addElementUsingSystemArrayCopy(sourceArray, elementToAdd);
+
+        Integer[] expectedArray = {1, 2, 3, 4, 5};
+        assertArrayEquals(expectedArray, destArray);
+    }
+}

core-java-collections-set/README.md

@@ -0,0 +1,11 @@
+=========
+
+## Core Java Sets Cookbooks and Examples
+
+### Relevant Articles: 
+- [Set Operations in Java](http://www.baeldung.com/set-operations-in-java)
+- [HashSet and TreeSet Comparison](http://www.baeldung.com/java-hashset-vs-treeset)
+- [A Guide to HashSet in Java](http://www.baeldung.com/java-hashset)
+- [A Guide to TreeSet in Java](http://www.baeldung.com/java-tree-set)
+- [Initializing HashSet at the Time of Construction](http://www.baeldung.com/java-initialize-hashset)
+- [Guide to EnumSet](https://www.baeldung.com/java-enumset)

core-java-collections-set/pom.xml

@@ -0,0 +1,33 @@
+<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>
+    <artifactId>core-java-collections-set</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-collections-set</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+    <dependency>
+        <groupId>com.google.guava</groupId>
+        <artifactId>guava</artifactId>
+        <version>${guava.version}</version>
+    </dependency>
+    <dependency>
+        <groupId>org.apache.commons</groupId>
+        <artifactId>commons-collections4</artifactId>
+        <version>${commons-collections4.version}</version>
+    </dependency>
+    </dependencies>
+
+    <properties>
+        <commons-collections4.version>4.3</commons-collections4.version>
+        <guava.version>27.1-jre</guava.version>
+    </properties>
+</project>

core-java-collections-set/src/test/java/com/baeldung/set/SetOperationsUnitTest.java

@@ -0,0 +1,93 @@
+package com.baeldung.set;
+
+import static org.junit.Assert.*;
+
+import org.apache.commons.collections4.SetUtils;
+import org.junit.Test;
+
+import com.google.common.collect.Sets;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class SetOperationsUnitTest {
+
+    private Set<Integer> setA = setOf(1,2,3,4);
+    private Set<Integer> setB = setOf(2,4,6,8);
+    
+    private static Set<Integer> setOf(Integer... values) {
+        return new HashSet<Integer>(Arrays.asList(values));
+    }
+    
+    @Test
+    public void givenTwoSets_WhenWeRetainAll_ThenWeIntersectThem() {
+        Set<Integer> intersectSet = new HashSet<>(setA);
+        intersectSet.retainAll(setB);
+        assertEquals(setOf(2,4), intersectSet);
+    }
+    
+    @Test
+    public void givenTwoSets_WhenWeAddAll_ThenWeUnionThem() {
+        Set<Integer> unionSet = new HashSet<>(setA);
+        unionSet.addAll(setB);
+        assertEquals(setOf(1,2,3,4,6,8), unionSet);
+    }
+    
+    @Test
+    public void givenTwoSets_WhenRemoveAll_ThenWeGetTheDifference() {
+        Set<Integer> differenceSet = new HashSet<>(setA);
+        differenceSet.removeAll(setB);
+        assertEquals(setOf(1,3), differenceSet);
+    }
+    
+    @Test
+    public void givenTwoStreams_WhenWeFilterThem_ThenWeCanGetTheIntersect() {
+        Set<Integer> intersectSet = setA.stream()
+            .filter(setB::contains)
+            .collect(Collectors.toSet());
+        assertEquals(setOf(2,4), intersectSet);
+    }
+    
+    @Test
+    public void givenTwoStreams_WhenWeConcatThem_ThenWeGetTheUnion() {
+        Set<Integer> unionSet = Stream.concat(setA.stream(), setB.stream())
+            .collect(Collectors.toSet());
+        assertEquals(setOf(1,2,3,4,6,8), unionSet);
+    }
+    
+    @Test
+    public void givenTwoStreams_WhenWeFilterThem_ThenWeCanGetTheDifference() {
+        Set<Integer> differenceSet = setA.stream()
+            .filter(val -> !setB.contains(val))
+            .collect(Collectors.toSet());
+        assertEquals(setOf(1,3), differenceSet);
+    }
+    
+    @Test
+    public void givenTwoSets_WhenWeUseApacheCommonsIntersect_ThenWeGetTheIntersect() {
+        Set<Integer> intersectSet = SetUtils.intersection(setA, setB);
+        assertEquals(setOf(2,4), intersectSet);
+    }
+    
+    @Test
+    public void givenTwoSets_WhenWeUseApacheCommonsUnion_ThenWeGetTheUnion() {
+        Set<Integer> unionSet = SetUtils.union(setA, setB);
+        assertEquals(setOf(1,2,3,4,6,8), unionSet);
+    }
+    
+    
+    @Test
+    public void givenTwoSets_WhenWeUseGuavaIntersect_ThenWeGetTheIntersect() {
+        Set<Integer> intersectSet = Sets.intersection(setA, setB);
+        assertEquals(setOf(2,4), intersectSet);
+    }
+    
+    @Test
+    public void givenTwoSets_WhenWeUseGuavaUnion_ThenWeGetTheUnion() {
+        Set<Integer> unionSet = Sets.union(setA, setB);
+        assertEquals(setOf(1,2,3,4,6,8), unionSet);
+    }
+}

core-java-collections/README.md

@@ -3,15 +3,11 @@
 ## Core Java Collections Cookbooks and Examples
 
 ### Relevant Articles: 
-- [Java - Combine Multiple Collections](http://www.baeldung.com/java-combine-multiple-collections)
-- [HashSet and TreeSet Comparison](http://www.baeldung.com/java-hashset-vs-treeset)
+- [Java – Combine Multiple Collections](http://www.baeldung.com/java-combine-multiple-collections)
 - [Collect a Java Stream to an Immutable Collection](http://www.baeldung.com/java-stream-immutable-collection)
 - [Introduction to the Java ArrayDeque](http://www.baeldung.com/java-array-deque)
-- [A Guide to HashSet in Java](http://www.baeldung.com/java-hashset)
-- [A Guide to TreeSet in Java](http://www.baeldung.com/java-tree-set)
 - [Getting the Size of an Iterable in Java](http://www.baeldung.com/java-iterable-size)
 - [How to Filter a Collection in Java](http://www.baeldung.com/java-collection-filtering)
-- [Initializing HashSet at the Time of Construction](http://www.baeldung.com/java-initialize-hashset)
 - [Removing the First Element of an Array](https://www.baeldung.com/java-array-remove-first-element)
 - [Fail-Safe Iterator vs Fail-Fast Iterator](http://www.baeldung.com/java-fail-safe-vs-fail-fast-iterator)
 - [Shuffling Collections In Java](http://www.baeldung.com/java-shuffle-collection)
@@ -23,7 +19,6 @@
 - [Time Complexity of Java Collections](https://www.baeldung.com/java-collections-complexity)
 - [Operating on and Removing an Item from Stream](https://www.baeldung.com/java-use-remove-item-stream)
 - [An Introduction to Synchronized Java Collections](https://www.baeldung.com/java-synchronized-collections)
-- [Guide to EnumSet](https://www.baeldung.com/java-enumset)
 - [Removing Elements from Java Collections](https://www.baeldung.com/java-collection-remove-elements)
 - [Combining Different Types of Collections in Java](https://www.baeldung.com/java-combine-collections)
 - [Sorting in Java](http://www.baeldung.com/java-sorting)
@@ -33,3 +28,4 @@
 - [Differences Between HashMap and Hashtable](https://www.baeldung.com/hashmap-hashtable-differences)
 - [Java ArrayList vs Vector](https://www.baeldung.com/java-arraylist-vs-vector)
 - [Defining a Char Stack in Java](https://www.baeldung.com/java-char-stack)
+- [Time Comparison of Arrays.sort(Object[]) and Arrays.sort(int[])](https://www.baeldung.com/arrays-sortobject-vs-sortint)

core-java-concurrency-advanced/README.md

@@ -12,7 +12,7 @@
 - [Guide to the Java Phaser](http://www.baeldung.com/java-phaser)
 - [An Introduction to Atomic Variables in Java](http://www.baeldung.com/java-atomic-variables)
 - [CyclicBarrier in Java](http://www.baeldung.com/java-cyclic-barrier)
-- [Guide to Volatile Keyword in Java](http://www.baeldung.com/java-volatile)
+- [Guide to the Volatile Keyword in Java](http://www.baeldung.com/java-volatile)
 - [Semaphores in Java](http://www.baeldung.com/java-semaphore)
 - [Daemon Threads in Java](http://www.baeldung.com/java-daemon-thread)
 - [Priority-based Job Scheduling in Java](http://www.baeldung.com/java-priority-job-schedule)
@@ -20,5 +20,6 @@
 - [Print Even and Odd Numbers Using 2 Threads](https://www.baeldung.com/java-even-odd-numbers-with-2-threads)
 - [Java CyclicBarrier vs CountDownLatch](https://www.baeldung.com/java-cyclicbarrier-countdownlatch)
 - [Guide to the Fork/Join Framework in Java](http://www.baeldung.com/java-fork-join)
-- [A Guide to ThreadLocalRandom in Java](http://www.baeldung.com/java-thread-local-random)
-- [The Thread.join() Method in Java](http://www.baeldung.com/java-thread-join)
+- [Guide to ThreadLocalRandom in Java](http://www.baeldung.com/java-thread-local-random)
+- [The Thread.join() Method in Java](http://www.baeldung.com/java-thread-join)
+- [Passing Parameters to Java Threads](https://www.baeldung.com/java-thread-parameters)

core-java-concurrency-basic/README.md

@@ -7,12 +7,13 @@
 - [A Guide to the Java ExecutorService](http://www.baeldung.com/java-executor-service-tutorial)
 - [Guide to java.util.concurrent.Future](http://www.baeldung.com/java-future)
 - [Difference Between Wait and Sleep in Java](http://www.baeldung.com/java-wait-and-sleep)
-- [Guide to Synchronized Keyword in Java](http://www.baeldung.com/java-synchronized)
+- [Guide to the Synchronized Keyword in Java](http://www.baeldung.com/java-synchronized)
 - [Overview of the java.util.concurrent](http://www.baeldung.com/java-util-concurrent)
 - [Implementing a Runnable vs Extending a Thread](http://www.baeldung.com/java-runnable-vs-extending-thread)
 - [How to Kill a Java Thread](http://www.baeldung.com/java-thread-stop)
-- [ExecutorService - Waiting for Threads to Finish](http://www.baeldung.com/java-executor-wait-for-threads)
+- [ExecutorService – Waiting for Threads to Finish](http://www.baeldung.com/java-executor-wait-for-threads)
 - [wait and notify() Methods in Java](http://www.baeldung.com/java-wait-notify)
 - [Life Cycle of a Thread in Java](http://www.baeldung.com/java-thread-lifecycle)
 - [Runnable vs. Callable in Java](http://www.baeldung.com/java-runnable-callable)
-- [What is Thread-Safety and How to Achieve it](https://www.baeldung.com/java-thread-safety)
+- [What is Thread-Safety and How to Achieve it?](https://www.baeldung.com/java-thread-safety)
+- [How to Start a Thread in Java](https://www.baeldung.com/java-start-thread)

core-java-io/README.md

@@ -6,7 +6,7 @@
 - [How to Read a Large File Efficiently with Java](http://www.baeldung.com/java-read-lines-large-file)
 - [Java InputStream to String](http://www.baeldung.com/convert-input-stream-to-string)
 - [Java – Write to File](http://www.baeldung.com/java-write-to-file)
-- [Java - Convert File to InputStream](http://www.baeldung.com/convert-file-to-input-stream)
+- [Java – Convert File to InputStream](http://www.baeldung.com/convert-file-to-input-stream)
 - [Java Scanner](http://www.baeldung.com/java-scanner)
 - [Java – Byte Array to Writer](http://www.baeldung.com/java-convert-byte-array-to-writer)
 - [Java – Directory Size](http://www.baeldung.com/java-folder-size)
@@ -14,7 +14,7 @@
 - [File Size in Java](http://www.baeldung.com/java-file-size)
 - [Comparing getPath(), getAbsolutePath(), and getCanonicalPath() in Java](http://www.baeldung.com/java-path)
 - [Using Java MappedByteBuffer](http://www.baeldung.com/java-mapped-byte-buffer)
-- [Copy a File with Java](http://www.baeldung.com/java-copy-file)
+- [How to Copy a File with Java](http://www.baeldung.com/java-copy-file)
 - [Java – Append Data to a File](http://www.baeldung.com/java-append-to-file)
 - [FileNotFoundException in Java](http://www.baeldung.com/java-filenotfound-exception)
 - [How to Read a File in Java](http://www.baeldung.com/reading-file-in-java)
@@ -30,7 +30,6 @@
 - [Download a File From an URL in Java](http://www.baeldung.com/java-download-file)
 - [Create a Symbolic Link with Java](http://www.baeldung.com/java-symlink)
 - [Quick Use of FilenameFilter](http://www.baeldung.com/java-filename-filter)
-- [Initialize a HashMap in Java](https://www.baeldung.com/java-initialize-hashmap)
 - [Read a File into an ArrayList](https://www.baeldung.com/java-file-to-arraylist)
 - [Guide to Java OutputStream](https://www.baeldung.com/java-outputstream)
 - [Reading a CSV File into an Array](https://www.baeldung.com/java-csv-file-array)
@@ -40,3 +39,4 @@
 - [Create a Directory in Java](https://www.baeldung.com/java-create-directory)
 - [How to Write to a CSV File in Java](https://www.baeldung.com/java-csv)
 - [List Files in a Directory in Java](https://www.baeldung.com/java-list-directory-files)
+- [Java InputStream to Byte Array and ByteBuffer](https://www.baeldung.com/convert-input-stream-to-array-of-bytes)

core-java-io/src/test/java/com/baeldung/filechannel/FileChannelUnitTest.java

@@ -0,0 +1,165 @@
+package com.baeldung.filechannel;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+import java.io.ByteArrayOutputStream;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.ByteBuffer;
+import java.nio.MappedByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.channels.FileLock;
+import java.nio.charset.StandardCharsets;
+
+import org.junit.Test;
+
+public class FileChannelUnitTest {
+
+    @Test
+    public void givenFile_whenReadWithFileChannelUsingRandomAccessFile_thenCorrect() throws IOException {
+
+        try (RandomAccessFile reader = new RandomAccessFile("src/test/resources/test_read.in", "r"); 
+            FileChannel channel = reader.getChannel(); 
+            ByteArrayOutputStream out = new ByteArrayOutputStream();) {
+
+            int bufferSize = 1024;
+            if (bufferSize > channel.size()) {
+                bufferSize = (int) channel.size();
+            }
+            ByteBuffer buff = ByteBuffer.allocate(bufferSize);
+
+            while (channel.read(buff) > 0) {
+                out.write(buff.array(), 0, buff.position());
+                buff.clear();
+            }
+
+            String fileContent = new String(out.toByteArray(), StandardCharsets.UTF_8);
+
+            assertEquals("Hello world", fileContent);
+        }
+    }
+
+    @Test
+    public void givenFile_whenReadWithFileChannelUsingFileInputStream_thenCorrect() throws IOException {
+
+        try (ByteArrayOutputStream out = new ByteArrayOutputStream(); 
+            FileInputStream fin = new FileInputStream("src/test/resources/test_read.in"); 
+            FileChannel channel = fin.getChannel();) {
+
+            int bufferSize = 1024;
+            if (bufferSize > channel.size()) {
+                bufferSize = (int) channel.size();
+            }
+            ByteBuffer buff = ByteBuffer.allocate(bufferSize);
+
+            while (channel.read(buff) > 0) {
+                out.write(buff.array(), 0, buff.position());
+                buff.clear();
+            }
+            String fileContent = new String(out.toByteArray(), StandardCharsets.UTF_8);
+
+            assertEquals("Hello world", fileContent);
+        }
+    }
+
+    @Test
+    public void givenFile_whenReadAFileSectionIntoMemoryWithFileChannel_thenCorrect() throws IOException {
+
+        try (RandomAccessFile reader = new RandomAccessFile("src/test/resources/test_read.in", "r"); 
+            FileChannel channel = reader.getChannel(); 
+            ByteArrayOutputStream out = new ByteArrayOutputStream();) {
+
+            MappedByteBuffer buff = channel.map(FileChannel.MapMode.READ_ONLY, 6, 5);
+
+            if (buff.hasRemaining()) {
+                byte[] data = new byte[buff.remaining()];
+                buff.get(data);
+                assertEquals("world", new String(data, StandardCharsets.UTF_8));
+            }
+        }
+    }
+
+    @Test
+    public void whenWriteWithFileChannelUsingRandomAccessFile_thenCorrect() throws IOException {
+        String file = "src/test/resources/test_write_using_filechannel.txt";
+        try (RandomAccessFile writer = new RandomAccessFile(file, "rw"); 
+            FileChannel channel = writer.getChannel();) {
+            ByteBuffer buff = ByteBuffer.wrap("Hello world".getBytes(StandardCharsets.UTF_8));
+
+            channel.write(buff);
+
+            // now we verify whether the file was written correctly
+            RandomAccessFile reader = new RandomAccessFile(file, "r");
+            assertEquals("Hello world", reader.readLine());
+            reader.close();
+        }
+    }
+
+    @Test
+    public void givenFile_whenWriteAFileUsingLockAFileSectionWithFileChannel_thenCorrect() throws IOException {
+        try (RandomAccessFile reader = new RandomAccessFile("src/test/resources/test_read.in", "rw"); 
+            FileChannel channel = reader.getChannel(); 
+            FileLock fileLock = channel.tryLock(6, 5, Boolean.FALSE);) {
+
+            assertNotNull(fileLock);
+        }
+    }
+
+    @Test
+    public void givenFile_whenReadWithFileChannelGetPosition_thenCorrect() throws IOException {
+
+        try (ByteArrayOutputStream out = new ByteArrayOutputStream(); 
+            RandomAccessFile reader = new RandomAccessFile("src/test/resources/test_read.in", "r"); 
+            FileChannel channel = reader.getChannel();) {
+
+            int bufferSize = 1024;
+            if (bufferSize > channel.size()) {
+                bufferSize = (int) channel.size();
+            }
+            ByteBuffer buff = ByteBuffer.allocate(bufferSize);
+
+            while (channel.read(buff) > 0) {
+                out.write(buff.array(), 0, buff.position());
+                buff.clear();
+            }
+
+            // the original file is 11 bytes long, so that's where the position pointer should be
+            assertEquals(11, channel.position());
+
+            channel.position(4);
+            assertEquals(4, channel.position());
+        }
+    }
+
+    @Test
+    public void whenGetFileSize_thenCorrect() throws IOException {
+
+        try (RandomAccessFile reader = new RandomAccessFile("src/test/resources/test_read.in", "r"); 
+            FileChannel channel = reader.getChannel();) {
+
+            // the original file is 11 bytes long, so that's where the position pointer should be
+            assertEquals(11, channel.size());
+        }
+    }
+
+    @Test
+    public void whenTruncateFile_thenCorrect() throws IOException {
+        String input = "this is a test input";
+
+        FileOutputStream fout = new FileOutputStream("src/test/resources/test_truncate.txt");
+        FileChannel channel = fout.getChannel();
+
+        ByteBuffer buff = ByteBuffer.wrap(input.getBytes());
+        channel.write(buff);
+        buff.flip();
+
+        channel = channel.truncate(5);
+        assertEquals(5, channel.size());
+
+        fout.close();
+        channel.close();
+    }
+}

core-java-io/src/test/resources/test_truncate.txt

@@ -0,0 +1 @@
+this