Merge remote-tracking branch 'upstream/master' into BAEL-2781-classgraph

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

@@ -30,7 +30,7 @@ public class TreeNode {
         this.leftChild = leftChild;
     }
 
-    public TreeNode(int value, TreeNode rightChild, TreeNode leftChild) {
+    public TreeNode(int value, TreeNode leftChild, TreeNode rightChild) {
         this.value = value;
         this.rightChild = rightChild;
         this.leftChild = leftChild;

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

@@ -4,21 +4,6 @@ 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;

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

@@ -10,7 +10,7 @@ public class TreeReverserUnitTest {
     public void givenTreeWhenReversingRecursivelyThenReversed() {
         TreeReverser reverser = new TreeReverser();
 
-        TreeNode treeNode = reverser.createBinaryTree();
+        TreeNode treeNode = createBinaryTree();
 
         reverser.reverseRecursive(treeNode);
 
@@ -22,7 +22,7 @@ public class TreeReverserUnitTest {
     public void givenTreeWhenReversingIterativelyThenReversed() {
         TreeReverser reverser = new TreeReverser();
 
-        TreeNode treeNode = reverser.createBinaryTree();
+        TreeNode treeNode = createBinaryTree();
 
         reverser.reverseIterative(treeNode);
 
@@ -30,4 +30,18 @@ public class TreeReverserUnitTest {
             .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;
+    }
 }

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>
+    <dependencies>
-        <cxf-version>3.2.0</cxf-version>
+        <dependency>
-    </properties>
+            <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>
+    <properties>
-        <dependency>
+        <cxf-version>3.2.0</cxf-version>
-            <groupId>org.apache.cxf</groupId>
+    </properties>
-            <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>
 
 </project>

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

@@ -13,11 +13,28 @@
         <version>0.0.1-SNAPSHOT</version>
     </parent>
 
-    <properties>
+    <dependencies>
-        <liberty-maven-plugin.version>2.4.2</liberty-maven-plugin.version>
+
-        <failOnMissingWebXml>false</failOnMissingWebXml>
+        <dependency>
-        <openliberty-version>18.0.0.2</openliberty-version>
+            <groupId>javax.ws.rs</groupId>
-    </properties>
+            <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>
+    <properties>
-
+        <liberty-maven-plugin.version>2.4.2</liberty-maven-plugin.version>
-        <dependency>
+        <failOnMissingWebXml>false</failOnMissingWebXml>
-            <groupId>javax.ws.rs</groupId>
+        <openliberty-version>18.0.0.2</openliberty-version>
-            <artifactId>javax.ws.rs-api</artifactId>
+    </properties>
-            <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>
 
 </project>

apache-meecrowave/pom.xml

@@ -7,6 +7,12 @@
     <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 -->
         <dependency>

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;

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`

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-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>
+    <parent>
-        <java.version>1.8</java.version>
+        <artifactId>parent-boot-2</artifactId>
-    </properties>
+        <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-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>
+    <parent>
-        <java.version>1.8</java.version>
+        <artifactId>parent-boot-2</artifactId>
-    </properties>
+        <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>

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/README.md

@@ -8,6 +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/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

@@ -6,3 +6,4 @@
 - [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/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

@@ -34,6 +34,7 @@
                 <configuration>
                     <source>${maven.compiler.source.version}</source>
                     <target>${maven.compiler.target.version}</target>
+                    <compilerArgs>--enable-preview</compilerArgs>
                 </configuration>
             </plugin>
         </plugins>

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);
-
-}