Merge branch 'master' of https://github.com/vikasrajput6035/tutorials into BAEL-4936

core-java-modules/core-java-10/README.md

@@ -5,7 +5,10 @@ This module contains articles about Java 10 core features
 ### Relevant Articles: 
 
 - [Java 10 LocalVariable Type-Inference](http://www.baeldung.com/java-10-local-variable-type-inference)
-- [Guide to Java 10](http://www.baeldung.com/java-10-overview)
+- [New Features in Java 10](https://www.baeldung.com/java-10-overview)
 - [Copy a List to Another List in Java](http://www.baeldung.com/java-copy-list-to-another)
 - [Deep Dive Into the New Java JIT Compiler – Graal](https://www.baeldung.com/graal-java-jit-compiler)
 - [Copying Sets in Java](https://www.baeldung.com/java-copy-sets)
+- [Converting between a List and a Set in Java](https://www.baeldung.com/convert-list-to-set-and-set-to-list)
+- [Java IndexOutOfBoundsException “Source Does Not Fit in Dest”](https://www.baeldung.com/java-indexoutofboundsexception)
+- [Collect a Java Stream to an Immutable Collection](https://www.baeldung.com/java-stream-immutable-collection)

core-java-modules/core-java-10/pom.xml

@@ -1,22 +1,29 @@
 <?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">
+        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-10</artifactId>
     <version>0.1.0-SNAPSHOT</version>
     <name>core-java-10</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>
-        <relativePath>../../</relativePath>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../</relativePath>
     </parent>
 
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>${commons-collections4.version}</version>
+        </dependency>
+    </dependencies>
+
     <build>
         <plugins>
             <plugin>
@@ -34,6 +41,7 @@
     <properties>
         <maven.compiler.source.version>10</maven.compiler.source.version>
         <maven.compiler.target.version>10</maven.compiler.target.version>
+        <commons-collections4.version>4.1</commons-collections4.version>
     </properties>
 
 </project>

core-java-modules/core-java-10/src/test/java/com/baeldung/AppUnitTest.java

@@ -7,7 +7,7 @@ import junit.framework.TestSuite;
 /**
  * Unit test for simple App.
  */
-public class AppTest 
+public class AppUnitTest
     extends TestCase
 {
     /**
@@ -15,7 +15,7 @@ public class AppTest
      *
      * @param testName name of the test case
      */
-    public AppTest( String testName )
+    public AppUnitTest(String testName )
     {
         super( testName );
     }
@@ -25,7 +25,7 @@ public class AppTest
      */
     public static Test suite()
     {
-        return new TestSuite( AppTest.class );
+        return new TestSuite( AppUnitTest.class );
     }
 
     /**

core-java-modules/core-java-10/src/test/java/com/baeldung/java10/collections/conversion/ListSetConversionUnitTest.java

@@ -0,0 +1,68 @@
+package com.baeldung.java10.collections.conversion;
+
+import com.google.common.collect.Lists;
+import com.google.common.collect.Sets;
+import org.apache.commons.collections4.CollectionUtils;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+public class ListSetConversionUnitTest {
+
+    // Set -> List; List -> Set
+
+    @Test
+    public final void givenUsingCoreJava_whenSetConvertedToList_thenCorrect() {
+        final Set<Integer> sourceSet = Sets.newHashSet(0, 1, 2, 3, 4, 5);
+        final List<Integer> targetList = new ArrayList<>(sourceSet);
+    }
+
+    @Test
+    public final void givenUsingCoreJava_whenListConvertedToSet_thenCorrect() {
+        final List<Integer> sourceList = Lists.newArrayList(0, 1, 2, 3, 4, 5);
+        final Set<Integer> targetSet = new HashSet<>(sourceList);
+    }
+
+    @Test
+    public void givenUsingJava10_whenSetConvertedToList_thenCorrect() {
+        final Set<Integer> sourceSet = Sets.newHashSet(0, 1, 2, 3, 4, 5);
+        final List<Integer> targetList = List.copyOf(sourceSet);
+    }
+
+    @Test
+    public void givenUsingJava10_whenListConvertedToSet_thenCorrect() {
+        final List<Integer> sourceList = Lists.newArrayList(0, 1, 2, 3, 4, 5);
+        final Set<Integer> targetSet = Set.copyOf(sourceList);
+    }
+
+    @Test
+    public final void givenUsingGuava_whenSetConvertedToList_thenCorrect() {
+        final Set<Integer> sourceSet = Sets.newHashSet(0, 1, 2, 3, 4, 5);
+        final List<Integer> targetList = Lists.newArrayList(sourceSet);
+    }
+
+    @Test
+    public final void givenUsingGuava_whenListConvertedToSet_thenCorrect() {
+        final List<Integer> sourceList = Lists.newArrayList(0, 1, 2, 3, 4, 5);
+        final Set<Integer> targetSet = Sets.newHashSet(sourceList);
+    }
+
+    @Test
+    public final void givenUsingCommonsCollections_whenListConvertedToSet_thenCorrect() {
+        final List<Integer> sourceList = Lists.newArrayList(0, 1, 2, 3, 4, 5);
+
+        final Set<Integer> targetSet = new HashSet<>(6);
+        CollectionUtils.addAll(targetSet, sourceList);
+    }
+
+    @Test
+    public final void givenUsingCommonsCollections_whenSetConvertedToList_thenCorrect() {
+        final Set<Integer> sourceSet = Sets.newHashSet(0, 1, 2, 3, 4, 5);
+
+        final List<Integer> targetList = new ArrayList<>(6);
+        CollectionUtils.addAll(targetList, sourceSet);
+    }
+}

core-java-modules/core-java-10/src/test/java/com/baeldung/java10/list/CopyListServiceUnitTest.java

@@ -10,5 +10,6 @@ public class CopyListServiceUnitTest {
     @Test(expected = UnsupportedOperationException.class)
     public void whenModifyCopyOfList_thenThrowsException() {
         List<Integer> copyList = List.copyOf(Arrays.asList(1, 2, 3, 4));
+        copyList.add(4);
     }
 }

core-java-modules/core-java-10/src/test/java/com/baeldung/java10/streams/StreamToImmutableJava10UnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.java10.streams;
+
+import static java.util.stream.Collectors.toUnmodifiableList;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.Test;
+
+public class StreamToImmutableJava10UnitTest {
+
+    @Test
+    public void whenUsingCollectorsToUnmodifiableList_thenSuccess() {
+        List<String> givenList = Arrays.asList("a", "b", "c");
+        List<String> result = givenList.stream()
+            .collect(toUnmodifiableList());
+
+        System.out.println(result.getClass());
+    }
+}

core-java-modules/core-java-11-2/README.md

@@ -0,0 +1,9 @@
+## Core Java 11
+
+This module contains articles about Java 11 core features
+
+### Relevant articles
+- [Guide to Java 8 Optional](https://www.baeldung.com/java-optional)
+- [Guide to Java Reflection](http://www.baeldung.com/java-reflection)
+- [Guide to Java 8’s Collectors](https://www.baeldung.com/java-8-collectors)
+- [New Features in Java 11](https://www.baeldung.com/java-11-new-features)

core-java-modules/core-java-11-2/pom.xml

@@ -0,0 +1,79 @@
+<?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-java-11-2</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-11-2</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>../..</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mock-server</groupId>
+            <artifactId>mockserver-junit-jupiter</artifactId>
+            <version>${mockserver.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <version>${junit.jupiter.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-params</artifactId>
+            <version>${junit.jupiter.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <version>${junit.jupiter.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>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <maven.compiler.source.version>11</maven.compiler.source.version>
+        <maven.compiler.target.version>11</maven.compiler.target.version>
+        <guava.version>29.0-jre</guava.version>
+        <junit.jupiter.version>5.7.0</junit.jupiter.version>
+        <assertj.version>3.17.2</assertj.version>
+        <mockserver.version>5.11.1</mockserver.version>
+    </properties>
+
+</project>

core-java-modules/core-java-11-2/src/main/java/com/baeldung/features/MainClass.java

@@ -0,0 +1,17 @@
+package com.baeldung.features;
+
+public class MainClass {
+
+    private static boolean mainPrivateMethod() {
+        return true;
+    }
+
+    public static class NestedClass {
+
+        boolean nestedPublicMethod() {
+            return mainPrivateMethod();
+        }
+
+    }
+
+}

core-java-modules/core-java-11-2/src/main/java/com/baeldung/reflection/Animal.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 public abstract class Animal implements Eating {
 

core-java-modules/core-java-11-2/src/main/java/com/baeldung/reflection/Bird.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 public class Bird extends Animal {
     private boolean walks;

core-java-modules/core-java-11-2/src/main/java/com/baeldung/reflection/DynamicGreeter.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 import java.lang.annotation.Annotation;
 

core-java-modules/core-java-11-2/src/main/java/com/baeldung/reflection/Eating.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 public interface Eating {
     String eats();

core-java-modules/core-java-11-2/src/main/java/com/baeldung/reflection/Goat.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 public class Goat extends Animal implements Locomotion {
 

core-java-modules/core-java-11-2/src/main/java/com/baeldung/reflection/Greeter.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;

core-java-modules/core-java-11-2/src/main/java/com/baeldung/reflection/GreetingAnnotation.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Field;

core-java-modules/core-java-11-2/src/main/java/com/baeldung/reflection/Greetings.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 @Greeter(greet="Good morning")
 public class Greetings {

core-java-modules/core-java-11-2/src/main/java/com/baeldung/reflection/Locomotion.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 public interface Locomotion {
     String getLocomotion();

core-java-modules/core-java-11-2/src/main/java/com/baeldung/reflection/Operations.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 public class Operations {
 

core-java-modules/core-java-11-2/src/main/java/com/baeldung/reflection/Person.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 public class Person {
     private String name;

core-java-modules/core-java-11-2/src/test/java/com/baeldung/collectors/Java8CollectorsUnitTest.java

@@ -1,18 +1,11 @@
-package com.baeldung.streams.collectors;
+package com.baeldung.collectors;
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Sets;
 import org.junit.Test;
 
-import java.util.Arrays;
-import java.util.Comparator;
-import java.util.DoubleSummaryStatistics;
-import java.util.LinkedList;
-import java.util.List;
-import java.util.Map;
-import java.util.Optional;
-import java.util.Set;
+import java.util.*;
 import java.util.function.BiConsumer;
 import java.util.function.BinaryOperator;
 import java.util.function.Function;
@@ -20,19 +13,7 @@ import java.util.function.Supplier;
 import java.util.stream.Collector;
 
 import static com.google.common.collect.Sets.newHashSet;
-import static java.util.stream.Collectors.averagingDouble;
-import static java.util.stream.Collectors.collectingAndThen;
-import static java.util.stream.Collectors.counting;
-import static java.util.stream.Collectors.groupingBy;
-import static java.util.stream.Collectors.joining;
-import static java.util.stream.Collectors.maxBy;
-import static java.util.stream.Collectors.partitioningBy;
-import static java.util.stream.Collectors.summarizingDouble;
-import static java.util.stream.Collectors.summingDouble;
-import static java.util.stream.Collectors.toCollection;
-import static java.util.stream.Collectors.toList;
-import static java.util.stream.Collectors.toMap;
-import static java.util.stream.Collectors.toSet;
+import static java.util.stream.Collectors.*;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
@@ -48,6 +29,14 @@ public class Java8CollectorsUnitTest {
         assertThat(result).containsAll(givenList);
     }
 
+    @Test
+    public void whenCollectingToUnmodifiableList_shouldCollectToUnmodifiableList() {
+        final List<String> result = givenList.stream().collect(toUnmodifiableList());
+
+        assertThatThrownBy(() -> result.add("foo"))
+          .isInstanceOf(UnsupportedOperationException.class);
+    }
+
     @Test
     public void whenCollectingToSet_shouldCollectToSet() throws Exception {
         final Set<String> result = givenList.stream().collect(toSet());
@@ -55,6 +44,14 @@ public class Java8CollectorsUnitTest {
         assertThat(result).containsAll(givenList);
     }
 
+    @Test
+    public void whenCollectingToUnmodifiableSet_shouldCollectToUnmodifiableSet() {
+        final Set<String> result = givenList.stream().collect(toUnmodifiableSet());
+
+        assertThatThrownBy(() -> result.add("foo"))
+          .isInstanceOf(UnsupportedOperationException.class);
+    }
+
     @Test
     public void givenContainsDuplicateElements_whenCollectingToSet_shouldAddDuplicateElementsOnlyOnce() throws Exception {
         final Set<String> result = listWithDuplicates.stream().collect(toSet());
@@ -84,6 +81,15 @@ public class Java8CollectorsUnitTest {
         assertThat(result).containsEntry("a", 1).containsEntry("bb", 2).containsEntry("ccc", 3).containsEntry("dd", 2);
     }
 
+    @Test
+    public void whenCollectingToUnmodifiableMap_shouldCollectToUnmodifiableMap() {
+        final Map<String, Integer> result = givenList.stream()
+          .collect(toUnmodifiableMap(Function.identity(), String::length));
+
+        assertThatThrownBy(() -> result.put("foo", 3))
+                .isInstanceOf(UnsupportedOperationException.class);
+    }
+
     @Test
     public void whenCollectingToMapwWithDuplicates_shouldCollectToMapMergingTheIdenticalItems() throws Exception {
         final Map<String, Integer> result = listWithDuplicates.stream().collect(

core-java-modules/core-java-11-2/src/test/java/com/baeldung/features/HttpClientIntegrationTest.java

@@ -0,0 +1,54 @@
+package com.baeldung.features;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.mockserver.integration.ClientAndServer;
+import org.mockserver.model.HttpStatusCode;
+import org.mockserver.socket.PortFactory;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.time.Duration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockserver.integration.ClientAndServer.startClientAndServer;
+
+class HttpClientIntegrationTest {
+
+    private static ClientAndServer mockServer;
+    private static int port;
+
+    @BeforeAll
+    static void startServer() {
+        port = PortFactory.findFreePort();
+        mockServer = startClientAndServer(port);
+        mockServer.when(new org.mockserver.model.HttpRequest().withMethod("GET"))
+          .respond(new org.mockserver.model.HttpResponse()
+            .withStatusCode(HttpStatusCode.OK_200.code())
+            .withBody("Hello from the server!"));
+    }
+
+    @AfterAll
+    static void stopServer() {
+        mockServer.stop();
+    }
+
+    @Test
+    void givenSampleHttpRequest_whenRequestIsSent_thenServerResponseIsReceived() throws IOException, InterruptedException {
+        HttpClient httpClient = HttpClient.newBuilder()
+          .version(HttpClient.Version.HTTP_2)
+          .connectTimeout(Duration.ofSeconds(20))
+          .build();
+        HttpRequest httpRequest = HttpRequest.newBuilder()
+          .GET()
+          .uri(URI.create("http://localhost:" + port))
+          .build();
+        HttpResponse<String> httpResponse = httpClient.send(httpRequest, HttpResponse.BodyHandlers.ofString());
+        assertThat(httpResponse.body()).isEqualTo("Hello from the server!");
+    }
+
+}

core-java-modules/core-java-11-2/src/test/java/com/baeldung/features/JavaElevenFeaturesUnitTest.java

@@ -0,0 +1,61 @@
+package com.baeldung.features;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import javax.annotation.Nonnull;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class JavaElevenFeaturesUnitTest {
+
+    @Test
+    void givenMultilineString_whenExtractingNonBlankStrippedLines_thenLinesAreReturned() {
+        String multilineString = "Baeldung helps \n \n developers \n explore Java.";
+        List<String> lines = multilineString.lines()
+          .filter(line -> !line.isBlank())
+          .map(String::strip)
+          .collect(Collectors.toList());
+        assertThat(lines).containsExactly("Baeldung helps", "developers", "explore Java.");
+    }
+
+    @Test
+    void givenTemporaryFile_whenReadingStringContent_thenContentIsReturned(@TempDir Path tempDir) throws IOException {
+        Path filePath = Files.writeString(Files.createTempFile(tempDir, "demo", ".txt"), "Sample text");
+        String fileContent = Files.readString(filePath);
+        assertThat(fileContent).isEqualTo("Sample text");
+    }
+
+    @Test
+    void givenSampleList_whenConvertingToArray_thenItemsRemainUnchanged() {
+        List<String> sampleList = Arrays.asList("Java", "Kotlin");
+        String[] sampleArray = sampleList.toArray(String[]::new);
+        assertThat(sampleArray).containsExactly("Java", "Kotlin");
+    }
+
+    @Test
+    void givenSampleList_whenConvertingToUppercaseString_thenUppercaseIsReturned() {
+        List<String> sampleList = Arrays.asList("Java", "Kotlin");
+        String resultString = sampleList.stream()
+          .map((@Nonnull var x) -> x.toUpperCase())
+          .collect(Collectors.joining(", "));
+        assertThat(resultString).isEqualTo("JAVA, KOTLIN");
+    }
+
+    @Test
+    void givenSampleList_whenExtractingNonBlankValues_thenOnlyNonBlanksAreReturned() {
+        List<String> sampleList = Arrays.asList("Java", "\n \n", "Kotlin", " ");
+        List<String> withoutBlanks = sampleList.stream()
+          .filter(Predicate.not(String::isBlank))
+          .collect(Collectors.toList());
+        assertThat(withoutBlanks).containsExactly("Java", "Kotlin");
+    }
+
+}

core-java-modules/core-java-11-2/src/test/java/com/baeldung/features/NestedClassesUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.features;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class NestedClassesUnitTest {
+
+    @Test
+    public void giveNestedClass_whenCallingMainClassPrivateMethod_thenNoExceptionIsThrown() {
+        MainClass.NestedClass nestedInstance = new MainClass.NestedClass();
+        assertThat(nestedInstance.nestedPublicMethod()).isTrue();
+    }
+
+    @Test
+    public void giveNestedClass_whenCheckingNestmate_thenNestedClassIsReturned() {
+        assertThat(MainClass.class.isNestmateOf(MainClass.NestedClass.class)).isTrue();
+    }
+
+    @Test
+    public void giveNestedClass_whenCheckingNestHost_thenMainClassIsReturned() {
+        assertThat(MainClass.NestedClass.class.getNestHost()).isEqualTo(MainClass.class);
+    }
+
+    @Test
+    public void giveNestedClass_whenCheckingNestMembers_thenNestMembersAreReturned() {
+        Set<String> nestedMembers = Arrays.stream(MainClass.NestedClass.class.getNestMembers())
+          .map(Class::getName)
+          .collect(Collectors.toSet());
+        assertThat(nestedMembers).contains(MainClass.class.getName(), MainClass.NestedClass.class.getName());
+    }
+
+}

core-java-modules/core-java-11-2/src/test/java/com/baeldung/optional/OptionalChainingUnitTest.java

@@ -7,7 +7,9 @@ import java.util.Optional;
 import java.util.function.Supplier;
 import java.util.stream.Stream;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
 
 public class OptionalChainingUnitTest {
 

core-java-modules/core-java-11-2/src/test/java/com/baeldung/optional/OptionalUnitTest.java

@@ -9,7 +9,9 @@ import java.util.List;
 import java.util.NoSuchElementException;
 import java.util.Optional;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
 
 public class OptionalUnitTest {
 
@@ -262,6 +264,12 @@ public class OptionalUnitTest {
             .orElseThrow(IllegalArgumentException::new);
     }
 
+    @Test(expected = NoSuchElementException.class)
+    public void whenNoArgOrElseThrowWorks_thenCorrect() {
+        String nullName = null;
+        String name = Optional.ofNullable(nullName).orElseThrow();
+    }
+
     public String getMyDefault() {
         LOG.debug("Getting default value...");
         return "Default Value";

core-java-modules/core-java-11-2/src/test/java/com/baeldung/reflection/OperationsUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.junit.Assert.assertFalse;

core-java-modules/core-java-11-2/src/test/java/com/baeldung/reflection/ReflectionUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.java.reflection;
+package com.baeldung.reflection;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -32,23 +32,23 @@ public class ReflectionUnitTest {
         final Class<?> clazz = goat.getClass();
 
         assertEquals("Goat", clazz.getSimpleName());
-        assertEquals("com.baeldung.java.reflection.Goat", clazz.getName());
-        assertEquals("com.baeldung.java.reflection.Goat", clazz.getCanonicalName());
+        assertEquals("com.baeldung.reflection.Goat", clazz.getName());
+        assertEquals("com.baeldung.reflection.Goat", clazz.getCanonicalName());
     }
 
     @Test
     public void givenClassName_whenCreatesObject_thenCorrect() throws ClassNotFoundException {
-        final Class<?> clazz = Class.forName("com.baeldung.java.reflection.Goat");
+        final Class<?> clazz = Class.forName("com.baeldung.reflection.Goat");
 
         assertEquals("Goat", clazz.getSimpleName());
-        assertEquals("com.baeldung.java.reflection.Goat", clazz.getName());
-        assertEquals("com.baeldung.java.reflection.Goat", clazz.getCanonicalName());
+        assertEquals("com.baeldung.reflection.Goat", clazz.getName());
+        assertEquals("com.baeldung.reflection.Goat", clazz.getCanonicalName());
     }
 
     @Test
     public void givenClass_whenRecognisesModifiers_thenCorrect() throws ClassNotFoundException {
-        final Class<?> goatClass = Class.forName("com.baeldung.java.reflection.Goat");
-        final Class<?> animalClass = Class.forName("com.baeldung.java.reflection.Animal");
+        final Class<?> goatClass = Class.forName("com.baeldung.reflection.Goat");
+        final Class<?> animalClass = Class.forName("com.baeldung.reflection.Animal");
         final int goatMods = goatClass.getModifiers();
         final int animalMods = animalClass.getModifiers();
 
@@ -63,7 +63,7 @@ public class ReflectionUnitTest {
         final Class<?> goatClass = goat.getClass();
         final Package pkg = goatClass.getPackage();
 
-        assertEquals("com.baeldung.java.reflection", pkg.getName());
+        assertEquals("com.baeldung.reflection", pkg.getName());
     }
 
     @Test
@@ -81,8 +81,8 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClass_whenGetsImplementedInterfaces_thenCorrect() throws ClassNotFoundException {
-        final Class<?> goatClass = Class.forName("com.baeldung.java.reflection.Goat");
-        final Class<?> animalClass = Class.forName("com.baeldung.java.reflection.Animal");
+        final Class<?> goatClass = Class.forName("com.baeldung.reflection.Goat");
+        final Class<?> animalClass = Class.forName("com.baeldung.reflection.Animal");
         final Class<?>[] goatInterfaces = goatClass.getInterfaces();
         final Class<?>[] animalInterfaces = animalClass.getInterfaces();
 
@@ -94,16 +94,16 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClass_whenGetsConstructor_thenCorrect() throws ClassNotFoundException {
-        final Class<?> goatClass = Class.forName("com.baeldung.java.reflection.Goat");
+        final Class<?> goatClass = Class.forName("com.baeldung.reflection.Goat");
         final Constructor<?>[] constructors = goatClass.getConstructors();
 
         assertEquals(1, constructors.length);
-        assertEquals("com.baeldung.java.reflection.Goat", constructors[0].getName());
+        assertEquals("com.baeldung.reflection.Goat", constructors[0].getName());
     }
 
     @Test
     public void givenClass_whenGetsFields_thenCorrect() throws ClassNotFoundException {
-        final Class<?> animalClass = Class.forName("com.baeldung.java.reflection.Animal");
+        final Class<?> animalClass = Class.forName("com.baeldung.reflection.Animal");
         final Field[] fields = animalClass.getDeclaredFields();
 
         final List<String> actualFields = getFieldNames(fields);
@@ -114,7 +114,7 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClass_whenGetsMethods_thenCorrect() throws ClassNotFoundException {
-        final Class<?> animalClass = Class.forName("com.baeldung.java.reflection.Animal");
+        final Class<?> animalClass = Class.forName("com.baeldung.reflection.Animal");
         final Method[] methods = animalClass.getDeclaredMethods();
         final List<String> actualMethods = getMethodNames(methods);
 
@@ -124,7 +124,7 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClass_whenGetsAllConstructors_thenCorrect() throws ClassNotFoundException {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
+        final Class<?> birdClass = Class.forName("com.baeldung.reflection.Bird");
         final Constructor<?>[] constructors = birdClass.getConstructors();
 
         assertEquals(3, constructors.length);
@@ -132,7 +132,7 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClass_whenGetsEachConstructorByParamTypes_thenCorrect() throws Exception {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
+        final Class<?> birdClass = Class.forName("com.baeldung.reflection.Bird");
         birdClass.getConstructor();
         birdClass.getConstructor(String.class);
         birdClass.getConstructor(String.class, boolean.class);
@@ -140,7 +140,7 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClass_whenInstantiatesObjectsAtRuntime_thenCorrect() throws Exception {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
+        final Class<?> birdClass = Class.forName("com.baeldung.reflection.Bird");
 
         final Constructor<?> cons1 = birdClass.getConstructor();
         final Constructor<?> cons2 = birdClass.getConstructor(String.class);
@@ -159,7 +159,7 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClass_whenGetsPublicFields_thenCorrect() throws ClassNotFoundException {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
+        final Class<?> birdClass = Class.forName("com.baeldung.reflection.Bird");
         final Field[] fields = birdClass.getFields();
         assertEquals(1, fields.length);
         assertEquals("CATEGORY", fields[0].getName());
@@ -168,7 +168,7 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClass_whenGetsPublicFieldByName_thenCorrect() throws Exception {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
+        final Class<?> birdClass = Class.forName("com.baeldung.reflection.Bird");
         final Field field = birdClass.getField("CATEGORY");
         assertEquals("CATEGORY", field.getName());
 
@@ -176,7 +176,7 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClass_whenGetsDeclaredFields_thenCorrect() throws ClassNotFoundException {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
+        final Class<?> birdClass = Class.forName("com.baeldung.reflection.Bird");
         final Field[] fields = birdClass.getDeclaredFields();
         assertEquals(1, fields.length);
         assertEquals("walks", fields[0].getName());
@@ -184,7 +184,7 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClass_whenGetsFieldsByName_thenCorrect() throws Exception {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
+        final Class<?> birdClass = Class.forName("com.baeldung.reflection.Bird");
         final Field field = birdClass.getDeclaredField("walks");
         assertEquals("walks", field.getName());
 
@@ -192,14 +192,14 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClassField_whenGetsType_thenCorrect() throws Exception {
-        final Field field = Class.forName("com.baeldung.java.reflection.Bird").getDeclaredField("walks");
+        final Field field = Class.forName("com.baeldung.reflection.Bird").getDeclaredField("walks");
         final Class<?> fieldClass = field.getType();
         assertEquals("boolean", fieldClass.getSimpleName());
     }
 
     @Test
     public void givenClassField_whenSetsAndGetsValue_thenCorrect() throws Exception {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
+        final Class<?> birdClass = Class.forName("com.baeldung.reflection.Bird");
         final Bird bird = (Bird) birdClass.getConstructor().newInstance();
         final Field field = birdClass.getDeclaredField("walks");
         field.setAccessible(true);
@@ -216,7 +216,7 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClassField_whenGetsAndSetsWithNull_thenCorrect() throws Exception {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
+        final Class<?> birdClass = Class.forName("com.baeldung.reflection.Bird");
         final Field field = birdClass.getField("CATEGORY");
         field.setAccessible(true);
 
@@ -225,7 +225,7 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClass_whenGetsAllPublicMethods_thenCorrect() throws ClassNotFoundException {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
+        final Class<?> birdClass = Class.forName("com.baeldung.reflection.Bird");
         final Method[] methods = birdClass.getMethods();
         final List<String> methodNames = getMethodNames(methods);
 
@@ -235,7 +235,7 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenClass_whenGetsOnlyDeclaredMethods_thenCorrect() throws ClassNotFoundException {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
+        final Class<?> birdClass = Class.forName("com.baeldung.reflection.Bird");
         final List<String> actualMethodNames = getMethodNames(birdClass.getDeclaredMethods());
 
         final List<String> expectedMethodNames = Arrays.asList("setWalks", "walks", "getSound", "eats");
@@ -248,24 +248,17 @@ public class ReflectionUnitTest {
 
     @Test
     public void givenMethodName_whenGetsMethod_thenCorrect() throws Exception {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
-        final Method walksMethod = birdClass.getDeclaredMethod("walks");
-        final Method setWalksMethod = birdClass.getDeclaredMethod("setWalks", boolean.class);
-
-        assertFalse(walksMethod.isAccessible());
-        assertFalse(setWalksMethod.isAccessible());
-
-        walksMethod.setAccessible(true);
-        setWalksMethod.setAccessible(true);
-
-        assertTrue(walksMethod.isAccessible());
-        assertTrue(setWalksMethod.isAccessible());
+        final Bird bird = new Bird();
+        final Method walksMethod = bird.getClass().getDeclaredMethod("walks");
+        final Method setWalksMethod = bird.getClass().getDeclaredMethod("setWalks", boolean.class);
 
+        assertTrue(walksMethod.canAccess(bird));
+        assertTrue(setWalksMethod.canAccess(bird));
     }
 
     @Test
     public void givenMethod_whenInvokes_thenCorrect() throws Exception {
-        final Class<?> birdClass = Class.forName("com.baeldung.java.reflection.Bird");
+        final Class<?> birdClass = Class.forName("com.baeldung.reflection.Bird");
         final Bird bird = (Bird) birdClass.getConstructor().newInstance();
         final Method setWalksMethod = birdClass.getDeclaredMethod("setWalks", boolean.class);
         final Method walksMethod = birdClass.getDeclaredMethod("walks");

core-java-modules/core-java-11/README.md

@@ -8,7 +8,7 @@ This module contains articles about Java 11 core features
 - [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)
+- [Exploring the New HTTP Client in Java](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)
 - [Negate a Predicate Method Reference with Java 11](https://www.baeldung.com/java-negate-predicate-method-reference)

core-java-modules/core-java-11/pom.xml

@@ -32,12 +32,12 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-core.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-generator.version}</version>
             <scope>provided</scope>
         </dependency>
         <dependency>
@@ -105,9 +105,8 @@
         <guava.version>27.1-jre</guava.version>
         <assertj.version>3.11.1</assertj.version>
         <uberjar.name>benchmarks</uberjar.name>
-        <jmh.version>1.22</jmh.version>
         <eclipse.collections.version>10.0.0</eclipse.collections.version>
-        <shade.plugin.version>10.0.0</shade.plugin.version>
+        <shade.plugin.version>3.2.4</shade.plugin.version>
     </properties>
 
 </project>

core-java-modules/core-java-11/src/test/java/com/baeldung/java11/httpclient/test/HttpClientUnitTest.java

@@ -64,7 +64,7 @@ public class HttpClientUnitTest {
             .send(request, HttpResponse.BodyHandlers.ofString());
 
         assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_MOVED_PERM));
-        assertThat(response.body(), containsString("https://stackoverflow.com/"));
+        assertTrue(response.headers().map().get("location").stream().anyMatch("https://stackoverflow.com/"::equals));
     }
 
     @Test

core-java-modules/core-java-11/src/test/java/com/baeldung/java11/httpclient/test/HttpRequestUnitTest.java

@@ -18,6 +18,7 @@ import java.security.NoSuchAlgorithmException;
 import java.time.Duration;
 
 import org.junit.Test;
+import org.junit.jupiter.api.Disabled;
 
 public class HttpRequestUnitTest {
 
@@ -48,7 +49,12 @@ public class HttpRequestUnitTest {
         assertThat(response.version(), equalTo(HttpClient.Version.HTTP_2));
     }
 
-    @Test
+    /*
+    * This test will fail as soon as the given URL returns a HTTP 2 response.
+    * Therefore, let's leave it commented out.
+    * */
+   @Test
+   @Disabled
     public void shouldFallbackToHttp1_1WhenWebsiteDoesNotUseHttp2() throws IOException, InterruptedException, URISyntaxException, NoSuchAlgorithmException {
         HttpRequest request = HttpRequest.newBuilder()
             .uri(new URI("https://postman-echo.com/get"))

core-java-modules/core-java-12/README.md

@@ -1,4 +1,4 @@
 ## Relevant Articles:
 
-
 - [String API Updates in Java 12](https://www.baeldung.com/java12-string-api)
+- [New Features in Java 12](https://www.baeldung.com/java-12-new-features)

core-java-modules/core-java-12/src/test/java/com/baeldung/newfeatures/CompactNumbersUnitTest.java

@@ -0,0 +1,21 @@
+package java.com.baeldung.newfeatures;
+
+import org.junit.Test;
+
+import java.text.NumberFormat;
+import java.util.Locale;
+
+import static org.junit.Assert.assertEquals;
+
+public class CompactNumbersUnitTest {
+
+    @Test
+    public void givenNumber_thenCompactValues() {
+        NumberFormat likesShort = NumberFormat.getCompactNumberInstance(new Locale("en", "US"), NumberFormat.Style.SHORT);
+        likesShort.setMaximumFractionDigits(2);
+        assertEquals("2.59K", likesShort.format(2592));
+        NumberFormat likesLong = NumberFormat.getCompactNumberInstance(new Locale("en", "US"), NumberFormat.Style.LONG);
+        likesLong.setMaximumFractionDigits(2);
+        assertEquals("2.59 thousand", likesShort.format(2592));
+    }
+}

core-java-modules/core-java-12/src/test/java/com/baeldung/newfeatures/FileMismatchUnitTest.java

@@ -0,0 +1,32 @@
+package java.com.baeldung.newfeatures;
+
+import org.junit.Test;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import static org.junit.Assert.assertEquals;
+
+public class FileMismatchUnitTest {
+
+    @Test
+    public void givenIdenticalFiles_thenShouldNotFindMismatch() throws IOException {
+        Path filePath1 = Files.createTempFile("file1", ".txt");
+        Path filePath2 = Files.createTempFile("file2", ".txt");
+        Files.writeString(filePath1, "Java 12 Article");
+        Files.writeString(filePath2, "Java 12 Article");
+        long mismatch = Files.mismatch(filePath1, filePath2);
+        assertEquals(-1, mismatch);
+    }
+
+    @Test
+    public void givenDifferentFiles_thenShouldFindMismatch() throws IOException {
+        Path filePath3 = Files.createTempFile("file3", ".txt");
+        Path filePath4 = Files.createTempFile("file4", ".txt");
+        Files.writeString(filePath3, "Java 12 Article");
+        Files.writeString(filePath4, "Java 12 Tutorial");
+        long mismatch = Files.mismatch(filePath3, filePath4);
+        assertEquals(8, mismatch);
+    }
+}

core-java-modules/core-java-12/src/test/java/com/baeldung/newfeatures/StringUnitTest.java

@@ -0,0 +1,15 @@
+package java.com.baeldung.newfeatures;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class StringUnitTest {
+
+    @Test
+    public void givenString_thenRevertValue() {
+        String text = "Baeldung";
+        String transformed = text.transform(value -> new StringBuilder(value).reverse().toString());
+        assertEquals("gnudleaB", transformed);
+    }
+}

core-java-modules/core-java-12/src/test/java/com/baeldung/newfeatures/TeeingCollectorUnitTest.java

@@ -0,0 +1,18 @@
+package java.com.baeldung.newfeatures;
+
+import org.junit.Test;
+
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static org.junit.Assert.assertEquals;
+
+public class TeeingCollectorUnitTest {
+
+    @Test
+    public void givenSetOfNumbers_thenCalculateAverage() {
+        double mean = Stream.of(1, 2, 3, 4, 5)
+          .collect(Collectors.teeing(Collectors.summingDouble(i -> i), Collectors.counting(), (sum, count) -> sum / count));
+        assertEquals(3.0, mean);
+    }
+}

core-java-modules/core-java-12/src/test/java/com/baeldung/string/StringAPIUnitTest.java

@@ -5,7 +5,7 @@ import static org.hamcrest.MatcherAssert.assertThat;
 
 import org.junit.Test;
 
-public class StringAPITest {
+public class StringAPIUnitTest {
 
     @Test
     public void whenPositiveArgument_thenReturnIndentedString() {

core-java-modules/core-java-13/README.md

@@ -1,4 +1,4 @@
 ### Relevant articles:
 
 - [Java Switch Statement](https://www.baeldung.com/java-switch)
-- [New Java 13 Features](https://www.baeldung.com/java-13-new-features)
+- [New Features in Java 13](https://www.baeldung.com/java-13-new-features)

core-java-modules/core-java-14/README.md

@@ -10,3 +10,4 @@ This module contains articles about Java 14.
 - [Helpful NullPointerExceptions in Java 14](https://www.baeldung.com/java-14-nullpointerexception)
 - [Foreign Memory Access API in Java 14](https://www.baeldung.com/java-foreign-memory-access)
 - [Java 14 Record Keyword](https://www.baeldung.com/java-record-keyword)
+- [New Features in Java 14](https://www.baeldung.com/java-14-new-features)

core-java-modules/core-java-14/pom.xml

@@ -44,6 +44,8 @@
                 <configuration>
                     <release>${maven.compiler.release}</release>
                     <compilerArgs>--enable-preview</compilerArgs>
+                    <source>14</source>
+                    <target>14</target>
                 </configuration>
             </plugin>
             <plugin>

core-java-modules/core-java-14/src/test/java/com/baeldung/java14/character/IsLetterOrAlphabetUnitTest.java

@@ -0,0 +1,30 @@
+package com.baeldung.java14.character;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.assertFalse;
+
+public class IsLetterOrAlphabetUnitTest {
+
+    @Test
+    public void givenACharacter_whenLetter_thenAssertIsLetterTrue() {
+        assertTrue(Character.isLetter(65));
+    }
+
+    @Test
+    public void givenACharacter_whenLetter_thenAssertIsAlphabeticTrue() {
+        assertTrue(Character.isAlphabetic(65));
+    }
+
+    @Test
+    public void givenACharacter_whenAlphabeticAndNotLetter_thenAssertIsLetterFalse() {
+        assertFalse(Character.isLetter(837));
+    }
+
+    @Test
+    public void givenACharacter_whenAlphabeticAndNotLetter_thenAssertIsAlphabeticTrue() {
+        assertTrue(Character.isAlphabetic(837));
+    }
+
+}

core-java-modules/core-java-14/src/test/java/com/baeldung/java14/newfeatues/MultilineUnitTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.java14.newfeatues;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class MultilineUnitTest {
+    
+    @SuppressWarnings("preview")
+    String multiline = """ 
+            A quick brown fox jumps over a lazy dog; \
+         the lazy dog howls loudly.""";
+    
+    @SuppressWarnings("preview")
+    String anotherMultiline = """ 
+            A quick brown fox jumps over a lazy dog; 
+         the lazy dog howls loudly.""";
+    
+    @Test
+    public void givenMultilineString_whenSlashUsed_thenNoNewLine() {
+        assertFalse(multiline.contains("\n"));
+        assertTrue(anotherMultiline.contains("\n"));
+    }
+
+}

core-java-modules/core-java-14/src/test/java/com/baeldung/java14/newfeatues/RecordUnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.java14.newfeatues;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class RecordUnitTest {
+
+    @SuppressWarnings("preview") 
+    public record User(int id, String password) {
+    };
+
+    private User user1 = new User(0, "UserOne");
+
+    @Test
+    public void givenRecord_whenObjInitialized_thenValuesCanBeFetchedWithGetters() {
+
+        assertEquals(0, user1.id());
+        assertEquals("UserOne", user1.password());
+    }
+
+    @Test
+    public void whenRecord_thenEqualsImplemented() {
+
+        User user2 = user1;
+
+        assertEquals(user1, user2);
+    }
+
+    @Test
+    public void whenRecord_thenToStringImplemented() {
+
+        assertTrue(user1.toString()
+            .contains("UserOne"));
+    }
+
+}

core-java-modules/core-java-14/src/test/java/com/baeldung/java14/newfeatues/SwitchExprUnitTest.java

@@ -0,0 +1,50 @@
+package com.baeldung.java14.newfeatues;
+
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class SwitchExprUnitTest {
+
+    @Test
+    public void givenDay_whenSunday_thenWeekend() {
+        assertTrue(isTodayHolidayInJava8("SUNDAY"));
+
+        assertTrue(isTodayHolidayInJava14("SUNDAY"));
+
+        assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> isTodayHolidayInJava8("SOMEDAY"));
+
+        assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> isTodayHolidayInJava14("SOMEDAY"));
+    }
+
+    private boolean isTodayHolidayInJava8(String day) {
+
+        boolean isTodayHoliday;
+        switch (day) {
+            case "MONDAY":
+            case "TUESDAY":
+            case "WEDNESDAY":
+            case "THURSDAY":
+            case "FRIDAY":
+                isTodayHoliday = false;
+                break;
+            case "SATURDAY":
+            case "SUNDAY":
+                isTodayHoliday = true;
+                break;
+            default:
+                throw new IllegalArgumentException("What's a " + day);
+        }
+        return isTodayHoliday;
+    }
+
+    private boolean isTodayHolidayInJava14(String day) {
+        return switch (day) {
+            case "MONDAY", "TUESDAY", "WEDNESDAY", "THURSDAY", "FRIDAY" -> false;
+            case "SATURDAY", "SUNDAY" -> true;
+            default -> throw new IllegalArgumentException("What's a " + day);
+        };
+    }
+
+}

core-java-modules/core-java-14/src/test/java/com/baeldung/java14/record/PersonUnitTest.java

@@ -7,7 +7,7 @@ import static org.junit.Assert.assertTrue;
 
 import org.junit.Test;
 
-public class PersonTest {
+public class PersonUnitTest {
 
     @Test
     public void givenSameNameAndAddress_whenEquals_thenPersonsEqual() {

core-java-modules/core-java-15/.mvn/jvm.config

@@ -0,0 +1 @@
+--enable-preview

core-java-modules/core-java-15/README.md

@@ -0,0 +1,7 @@
+## Core Java 15
+
+This module contains articles about Java 15. 
+
+### Relevant articles
+
+- [Sealed Classes and Interfaces in Java 15](https://www.baeldung.com/java-sealed-classes-interfaces)

core-java-modules/core-java-15/pom.xml

@@ -0,0 +1,76 @@
+<?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-java-15</artifactId>
+    <name>core-java-15</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>
+        <relativePath>../../pom.xml</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <version>${junit-jupiter.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <version>${junit-jupiter.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <release>${maven.compiler.release}</release>
+                    <compilerArgs>--enable-preview</compilerArgs>
+                    <source>14</source>
+                    <target>14</target>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>${surefire.plugin.version}</version>
+                <configuration>
+                    <argLine>--enable-preview</argLine>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <maven.compiler.release>15</maven.compiler.release>
+        <assertj.version>3.17.2</assertj.version>
+        <maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
+        <surefire.plugin.version>3.0.0-M3</surefire.plugin.version>
+    </properties>
+
+</project>

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/alternative/Vehicles.java

@@ -0,0 +1,49 @@
+package com.baeldung.sealed.alternative;
+
+public class Vehicles {
+
+    abstract static class Vehicle {
+
+        private final String registrationNumber;
+
+        public Vehicle(String registrationNumber) {
+            this.registrationNumber = registrationNumber;
+        }
+
+        public String getRegistrationNumber() {
+            return registrationNumber;
+        }
+
+    }
+
+    public static final class Car extends Vehicle {
+
+        private final int numberOfSeats;
+
+        public Car(int numberOfSeats, String registrationNumber) {
+            super(registrationNumber);
+            this.numberOfSeats = numberOfSeats;
+        }
+
+        public int getNumberOfSeats() {
+            return numberOfSeats;
+        }
+
+    }
+
+    public static final class Truck extends Vehicle {
+
+        private final int loadCapacity;
+
+        public Truck(int loadCapacity, String registrationNumber) {
+            super(registrationNumber);
+            this.loadCapacity = loadCapacity;
+        }
+
+        public int getLoadCapacity() {
+            return loadCapacity;
+        }
+
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/classes/Car.java

@@ -0,0 +1,21 @@
+package com.baeldung.sealed.classes;
+
+public non-sealed class Car extends Vehicle implements Service {
+
+    private final int numberOfSeats;
+
+    public Car(int numberOfSeats, String registrationNumber) {
+        super(registrationNumber);
+        this.numberOfSeats = numberOfSeats;
+    }
+
+    public int getNumberOfSeats() {
+        return numberOfSeats;
+    }
+
+    @Override
+    public int getMaxServiceIntervalInMonths() {
+        return 12;
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/classes/Service.java

@@ -0,0 +1,11 @@
+package com.baeldung.sealed.classes;
+
+public sealed interface Service permits Car, Truck {
+
+    int getMaxServiceIntervalInMonths();
+
+    default int getMaxDistanceBetweenServicesInKilometers() {
+        return 100000;
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/classes/Truck.java

@@ -0,0 +1,21 @@
+package com.baeldung.sealed.classes;
+
+public final class Truck extends Vehicle implements Service {
+
+    private final int loadCapacity;
+
+    public Truck(int loadCapacity, String registrationNumber) {
+        super(registrationNumber);
+        this.loadCapacity = loadCapacity;
+    }
+
+    public int getLoadCapacity() {
+        return loadCapacity;
+    }
+
+    @Override
+    public int getMaxServiceIntervalInMonths() {
+        return 18;
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/classes/Vehicle.java

@@ -0,0 +1,15 @@
+package com.baeldung.sealed.classes;
+
+public abstract sealed class Vehicle permits Car, Truck {
+
+    protected final String registrationNumber;
+
+    public Vehicle(String registrationNumber) {
+        this.registrationNumber = registrationNumber;
+    }
+
+    public String getRegistrationNumber() {
+        return registrationNumber;
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/records/Car.java

@@ -0,0 +1,14 @@
+package com.baeldung.sealed.records;
+
+public record Car(int numberOfSeats, String registrationNumber) implements Vehicle {
+
+    @Override
+    public String getRegistrationNumber() {
+        return registrationNumber;
+    }
+
+    public int getNumberOfSeats() {
+        return numberOfSeats;
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/records/Truck.java

@@ -0,0 +1,14 @@
+package com.baeldung.sealed.records;
+
+public record Truck(int loadCapacity, String registrationNumber) implements Vehicle {
+
+    @Override
+    public String getRegistrationNumber() {
+        return registrationNumber;
+    }
+
+    public int getLoadCapacity() {
+        return loadCapacity;
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/records/Vehicle.java

@@ -0,0 +1,7 @@
+package com.baeldung.sealed.records;
+
+public sealed interface Vehicle permits Car, Truck {
+
+    String getRegistrationNumber();
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/whatsnew/records/Person.java

@@ -0,0 +1,15 @@
+package com.baeldung.whatsnew.records;
+
+/**
+ * Java record with a header indicating 2 fields.
+ */
+public record Person(String name, int age) {
+    /**
+     * Public constructor that does some basic validation.
+     */
+    public Person {
+        if (age < 0) {
+            throw new IllegalArgumentException("Age cannot be negative");
+        }
+    }
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/whatsnew/sealedclasses/Employee.java

@@ -0,0 +1,9 @@
+package com.baeldung.whatsnew.sealedclasses;
+
+import java.util.Date;
+
+public non-sealed class Employee extends Person {
+    public Date getHiredDate() {
+        return new Date();
+    }
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/whatsnew/sealedclasses/Manager.java

@@ -0,0 +1,4 @@
+package com.baeldung.whatsnew.sealedclasses;
+
+public final class Manager extends Person {
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/whatsnew/sealedclasses/Person.java

@@ -0,0 +1,21 @@
+package com.baeldung.whatsnew.sealedclasses;
+
+import java.util.Date;
+
+public sealed class Person permits Employee, Manager {
+    /**
+     * Demonstration of pattern matching for instanceof
+     *
+     * @param person A Person object
+     * @return
+     */
+    public static void patternMatchingDemo(Person person) {
+        if(person instanceof Employee employee) {
+            Date hiredDate = employee.getHiredDate();
+        }
+
+        if(person instanceof Employee employee && employee.getHiredDate() != null) {
+            Date hiredDate = employee.getHiredDate();
+        }
+    }
+}

core-java-modules/core-java-15/src/test/java/com/baeldung/sealed/classes/VehicleUnitTest.java

@@ -0,0 +1,76 @@
+package com.baeldung.sealed.classes;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.lang.constant.ClassDesc;
+
+public class VehicleUnitTest {
+
+    private static Vehicle car;
+    private static Vehicle truck;
+
+    @BeforeAll
+    public static void createInstances() {
+        car = new Car(5, "VZ500DA");
+        truck = new Truck(19000, "VZ600TA");
+    }
+
+    @Test
+    public void givenCar_whenUsingReflectionAPI_thenSuperClassIsSealed() {
+        Assertions.assertThat(car.getClass().isSealed()).isEqualTo(false);
+        Assertions.assertThat(car.getClass().getSuperclass().isSealed()).isEqualTo(true);
+        Assertions.assertThat(car.getClass().getSuperclass().permittedSubclasses())
+                .contains(ClassDesc.of(car.getClass().getCanonicalName()));
+    }
+
+    @Test
+    public void givenTruck_whenUsingReflectionAPI_thenSuperClassIsSealed() {
+        Assertions.assertThat(truck.getClass().isSealed()).isEqualTo(false);
+        Assertions.assertThat(truck.getClass().getSuperclass().isSealed()).isEqualTo(true);
+        Assertions.assertThat(truck.getClass().getSuperclass().permittedSubclasses())
+                .contains(ClassDesc.of(truck.getClass().getCanonicalName()));
+    }
+
+    @Test
+    public void givenCar_whenGettingPropertyTraditionalWay_thenNumberOfSeatsPropertyIsReturned() {
+        Assertions.assertThat(getPropertyTraditionalWay(car)).isEqualTo(5);
+    }
+
+    @Test
+    public void givenCar_whenGettingPropertyViaPatternMatching_thenNumberOfSeatsPropertyIsReturned() {
+        Assertions.assertThat(getPropertyViaPatternMatching(car)).isEqualTo(5);
+    }
+
+    @Test
+    public void givenTruck_whenGettingPropertyTraditionalWay_thenLoadCapacityIsReturned() {
+        Assertions.assertThat(getPropertyTraditionalWay(truck)).isEqualTo(19000);
+    }
+
+    @Test
+    public void givenTruck_whenGettingPropertyViaPatternMatching_thenLoadCapacityIsReturned() {
+        Assertions.assertThat(getPropertyViaPatternMatching(truck)).isEqualTo(19000);
+    }
+
+    private int getPropertyTraditionalWay(Vehicle vehicle) {
+        if (vehicle instanceof Car) {
+            return ((Car) vehicle).getNumberOfSeats();
+        } else if (vehicle instanceof Truck) {
+            return ((Truck) vehicle).getLoadCapacity();
+        } else {
+            throw new RuntimeException("Unknown instance of Vehicle");
+        }
+    }
+
+    private int getPropertyViaPatternMatching(Vehicle vehicle) {
+        if (vehicle instanceof Car car) {
+            return car.getNumberOfSeats();
+        } else if (vehicle instanceof Truck truck) {
+            return truck.getLoadCapacity();
+        } else {
+            throw new RuntimeException("Unknown instance of Vehicle");
+        }
+    }
+
+}

core-java-modules/core-java-15/src/test/java/com/baeldung/sealed/records/VehicleUnitTest.java

@@ -0,0 +1,76 @@
+package com.baeldung.sealed.records;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.lang.constant.ClassDesc;
+
+public class VehicleUnitTest {
+
+    private static Vehicle car;
+    private static Vehicle truck;
+
+    @BeforeAll
+    public static void createInstances() {
+        car = new Car(4, "VZ500DA");
+        truck = new Truck(16000, "VZ600TA");
+    }
+
+    @Test
+    public void givenCar_whenUsingReflectionAPI_thenInterfaceIsSealed() {
+        Assertions.assertThat(car.getClass().isSealed()).isEqualTo(false);
+        Assertions.assertThat(car.getClass().getInterfaces()[0].isSealed()).isEqualTo(true);
+        Assertions.assertThat(car.getClass().getInterfaces()[0].permittedSubclasses())
+                .contains(ClassDesc.of(car.getClass().getCanonicalName()));
+    }
+
+    @Test
+    public void givenTruck_whenUsingReflectionAPI_thenInterfaceIsSealed() {
+        Assertions.assertThat(truck.getClass().isSealed()).isEqualTo(false);
+        Assertions.assertThat(truck.getClass().getInterfaces()[0].isSealed()).isEqualTo(true);
+        Assertions.assertThat(truck.getClass().getInterfaces()[0].permittedSubclasses())
+                .contains(ClassDesc.of(truck.getClass().getCanonicalName()));
+    }
+
+    @Test
+    public void givenCar_whenGettingPropertyTraditionalWay_thenNumberOfSeatsPropertyIsReturned() {
+        Assertions.assertThat(getPropertyTraditionalWay(car)).isEqualTo(4);
+    }
+
+    @Test
+    public void givenCar_whenGettingPropertyViaPatternMatching_thenNumberOfSeatsPropertyIsReturned() {
+        Assertions.assertThat(getPropertyViaPatternMatching(car)).isEqualTo(4);
+    }
+
+    @Test
+    public void givenTruck_whenGettingPropertyTraditionalWay_thenLoadCapacityIsReturned() {
+        Assertions.assertThat(getPropertyTraditionalWay(truck)).isEqualTo(16000);
+    }
+
+    @Test
+    public void givenTruck_whenGettingPropertyViaPatternMatching_thenLoadCapacityIsReturned() {
+        Assertions.assertThat(getPropertyViaPatternMatching(truck)).isEqualTo(16000);
+    }
+
+    private int getPropertyTraditionalWay(Vehicle vehicle) {
+        if (vehicle instanceof Car) {
+            return ((Car) vehicle).getNumberOfSeats();
+        } else if (vehicle instanceof Truck) {
+            return ((Truck) vehicle).getLoadCapacity();
+        } else {
+            throw new RuntimeException("Unknown instance of Vehicle");
+        }
+    }
+
+    private int getPropertyViaPatternMatching(Vehicle vehicle) {
+        if (vehicle instanceof Car car) {
+            return car.getNumberOfSeats();
+        } else if (vehicle instanceof Truck truck) {
+            return truck.getLoadCapacity();
+        } else {
+            throw new RuntimeException("Unknown instance of Vehicle");
+        }
+    }
+
+}

core-java-modules/core-java-8-datetime/src/test/java/com/baeldung/datetime/UseDateTimeFormatterUnitTest.java

@@ -31,6 +31,6 @@ public class UseDateTimeFormatterUnitTest {
     public void givenALocalDate_whenFormattingWithStyleAndLocale_thenPass() {
         String result = subject.formatWithStyleAndLocale(localDateTime, FormatStyle.MEDIUM, Locale.UK);
 
-        assertThat(result).isEqualTo("25 Jan 2015, 06:30:00");
+        assertThat(result).isEqualTo("25-Jan-2015 06:30:00");
     }
 }

core-java-modules/core-java-8-datetime/src/test/java/com/baeldung/datetime/UseToInstantUnitTest.java

@@ -3,6 +3,7 @@ package com.baeldung.datetime;
 import static org.assertj.core.api.Assertions.assertThat;
 
 import java.time.LocalDateTime;
+import java.time.ZoneId;
 import java.util.Calendar;
 import java.util.Date;
 import java.util.GregorianCalendar;
@@ -24,10 +25,11 @@ public class UseToInstantUnitTest {
 
     @Test
     public void givenADate_whenConvertingToLocalDate_thenAsExpected() {
-        Date givenDate = new Date(1465817690000L);
+        LocalDateTime currentDateTime = LocalDateTime.now();
+        Date givenDate = Date.from(currentDateTime.atZone(ZoneId.systemDefault()).toInstant());
 
         LocalDateTime localDateTime = subject.convertDateToLocalDate(givenDate);
 
-        assertThat(localDateTime).isEqualTo("2016-06-13T13:34:50");
+        assertThat(localDateTime).isEqualTo(currentDateTime);
     }
 }

core-java-modules/core-java-8-datetime/src/test/java/com/baeldung/datetime/UseZonedDateTimeUnitTest.java

@@ -54,7 +54,7 @@ public class UseZonedDateTimeUnitTest {
     @Test
     public void givenAStringWithTimeZone_whenParsing_thenEqualsExpected() {
         ZonedDateTime resultFromString = zonedDateTime.getZonedDateTimeUsingParseMethod("2015-05-03T10:15:30+01:00[Europe/Paris]");
-        ZonedDateTime resultFromLocalDateTime = ZonedDateTime.of(2015, 5, 3, 11, 15, 30, 0, ZoneId.of("Europe/Paris"));
+        ZonedDateTime resultFromLocalDateTime = ZonedDateTime.of(2015, 5, 3, 10, 15, 30, 0, ZoneId.of("Europe/Paris"));
 
         assertThat(resultFromString.getZone()).isEqualTo(ZoneId.of("Europe/Paris"));
         assertThat(resultFromLocalDateTime.getZone()).isEqualTo(ZoneId.of("Europe/Paris"));

core-java-modules/core-java-9-jigsaw/src/modules/com.baeldung.student.service.dbimpl/com/baeldung/student/service/dbimpl/StudentDbService.java

@@ -19,12 +19,12 @@ public class StudentDbService implements StudentService {
     }
 
     public Student update(Student student) {
-        logger.log(Level.INFO, "Updating sutdent in DB...");
+        logger.log(Level.INFO, "Updating student in DB...");
         return student;
     }
 
     public String delete(String registrationId) {
-        logger.log(Level.INFO, "Deleteing sutdent in DB...");
+        logger.log(Level.INFO, "Deleting student in DB...");
         return registrationId;
     }
 }

core-java-modules/core-java-9-jigsaw/src/simple-modules/main.app/com/baeldung/modules/main/MainApp.java

@@ -1,12 +1,15 @@
 package com.baeldung.modules.main;
 
+import com.baeldung.modules.hello.HelloInterface;
 import com.baeldung.modules.hello.HelloModules;
+import java.util.ServiceLoader;
 
 public class MainApp {
     public static void main(String[] args) {
         HelloModules.doSomething();
-
-        HelloModules module = new HelloModules();
-        module.sayHello();
+        
+        Iterable<HelloInterface> services = ServiceLoader.load(HelloInterface.class);
+        HelloInterface service = services.iterator().next();
+        service.sayHello();
     }
 }

core-java-modules/core-java-9-jigsaw/src/test/java/com/baeldung/java9/modules/ModuleAPIUnitTest.java

@@ -2,8 +2,7 @@ package com.baeldung.java9.modules;
 
 import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.CoreMatchers.nullValue;
-import static org.hamcrest.Matchers.contains;
-import static org.hamcrest.Matchers.containsInAnyOrder;
+import static org.hamcrest.Matchers.*;
 import static org.hamcrest.collection.IsEmptyCollection.empty;
 import static org.junit.Assert.*;
 
@@ -74,7 +73,6 @@ public class ModuleAPIUnitTest {
         ModuleLayer javaBaseModuleLayer = javaBaseModule.getLayer();
 
         assertTrue(javaBaseModuleLayer.configuration().findModule(JAVA_BASE_MODULE_NAME).isPresent());
-        assertThat(javaBaseModuleLayer.configuration().modules().size(), is(78));
         assertTrue(javaBaseModuleLayer.parents().get(0).configuration().parents().isEmpty());
     }
 
@@ -108,8 +106,7 @@ public class ModuleAPIUnitTest {
           .collect(Collectors.toSet());
 
         assertThat(javaBaseRequires, empty());
-        assertThat(javaSqlRequires.size(), is(3));
-        assertThat(javaSqlRequiresNames, containsInAnyOrder("java.base", "java.xml", "java.logging"));
+        assertThat(javaSqlRequiresNames, hasItems("java.base", "java.xml", "java.logging"));
     }
 
     @Test
@@ -127,16 +124,13 @@ public class ModuleAPIUnitTest {
 
     @Test
     public void givenModules_whenAccessingModuleDescriptorExports_thenExportsAreReturned() {
-        Set<Exports> javaBaseExports = javaBaseModule.getDescriptor().exports();
         Set<Exports> javaSqlExports = javaSqlModule.getDescriptor().exports();
 
         Set<String> javaSqlExportsSource = javaSqlExports.stream()
           .map(Exports::source)
           .collect(Collectors.toSet());
 
-        assertThat(javaBaseExports.size(), is(108));
-        assertThat(javaSqlExports.size(), is(3));
-        assertThat(javaSqlExportsSource, containsInAnyOrder("java.sql", "javax.transaction.xa", "javax.sql"));
+        assertThat(javaSqlExportsSource, hasItems("java.sql",  "javax.sql"));
     }
 
     @Test
@@ -144,7 +138,6 @@ public class ModuleAPIUnitTest {
         Set<String> javaBaseUses = javaBaseModule.getDescriptor().uses();
         Set<String> javaSqlUses = javaSqlModule.getDescriptor().uses();
 
-        assertThat(javaBaseUses.size(), is(34));
         assertThat(javaSqlUses, contains("java.sql.Driver"));
     }
 

core-java-modules/core-java-9-new-features/README.md

@@ -4,7 +4,7 @@ This module contains articles about core Java features that have been introduced
 
 ### Relevant Articles:
 
-- [Java 9 New Features](https://www.baeldung.com/new-java-9)
+- [New Features in Java 9](https://www.baeldung.com/new-java-9)
 - [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)
 - [Multi-Release Jar Files](https://www.baeldung.com/java-multi-release-jar)
@@ -13,3 +13,5 @@ This module contains articles about core Java features that have been introduced
 - [Java 9 Platform Logging API](https://www.baeldung.com/java-9-logging-api)
 - [Java 9 Reactive Streams](https://www.baeldung.com/java-9-reactive-streams)
 - [Multi-Release JAR Files with Maven](https://www.baeldung.com/maven-multi-release-jars)
+- [The Difference between RxJava API and the Java 9 Flow API](https://www.baeldung.com/rxjava-vs-java-flow-api)
+- [How to Get a Name of a Method Being Executed?](https://www.baeldung.com/java-name-of-executing-method)

core-java-modules/core-java-9/README.md

@@ -9,3 +9,4 @@ This module contains articles about Java 9 core features
 - [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)
 - [Immutable ArrayList in Java](https://www.baeldung.com/java-immutable-list)
+- [Easy Ways to Write a Java InputStream to an OutputStream](https://www.baeldung.com/java-inputstream-to-outputstream)

core-java-modules/core-java-9/pom.xml

@@ -44,6 +44,16 @@
             <artifactId>commons-collections4</artifactId>
             <version>${commons-collections4.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>commons-io</groupId>
+            <artifactId>commons-io</artifactId>
+            <version>${commons-io.version}</version>
+        </dependency>
     </dependencies>
 
     <build>
@@ -77,6 +87,7 @@
         <maven.compiler.target>1.9</maven.compiler.target>
         <guava.version>25.1-jre</guava.version>
         <commons-collections4.version>4.1</commons-collections4.version>
+        <commons-collections3.version>3.2.2</commons-collections3.version>
     </properties>
 
 </project>

core-java-modules/core-java-9/src/test/java/com/baeldung/java9/methodhandles/MethodHandlesUnitTest.java

@@ -17,7 +17,7 @@ import org.junit.Test;
 /**
  * Test case for the {@link MethodHandles} API
  */
-public class MethodHandlesTest {
+public class MethodHandlesUnitTest {
 
     @Test
     public void givenConcatMethodHandle_whenInvoked_thenCorrectlyConcatenated() throws Throwable {

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/AnnotatedClass.java

@@ -0,0 +1,8 @@
+package com.baeldung.annotations;
+
+import javax.annotation.Generated;
+
+@RetentionAnnotation
+@Generated("Available only on source code")
+public class AnnotatedClass {
+}

core-java-modules/core-java-annotations/src/main/java/com/baeldung/annotations/RetentionAnnotation.java

@@ -0,0 +1,12 @@
+package com.baeldung.annotations;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import static java.lang.annotation.ElementType.TYPE;
+
+@Target(TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface RetentionAnnotation {
+}

core-java-modules/core-java-annotations/src/test/java/com/baeldung/annotations/AnnotatedClassUnitTest.java

@@ -0,0 +1,18 @@
+package com.baeldung.annotations;
+
+import org.junit.Test;
+
+import java.lang.annotation.Annotation;
+
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThat;
+
+public class AnnotatedClassUnitTest {
+
+    @Test
+    public void whenAnnotationRetentionPolicyRuntime_shouldAccess() {
+        AnnotatedClass anAnnotatedClass = new AnnotatedClass();
+        Annotation[] annotations = anAnnotatedClass.getClass().getAnnotations();
+        assertThat(annotations.length, is(1));
+    }
+}

core-java-modules/core-java-annotations/src/test/java/com/baeldung/customannotations/ObjectToJsonConverterUnitTest.java

@@ -5,7 +5,7 @@ import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import org.junit.jupiter.api.Test;
 
-public class JsonSerializerUnitTest {
+public class ObjectToJsonConverterUnitTest {
 
     @Test
     public void givenObjectNotSerializedThenExceptionThrown() throws JsonSerializationException {

core-java-modules/core-java-arrays-guides/README.md

@@ -5,4 +5,6 @@ This module contains complete guides about arrays in Java
 ### Relevant Articles: 
 - [Arrays in Java: A Reference Guide](https://www.baeldung.com/java-arrays-guide)
 - [Guide to the java.util.Arrays Class](https://www.baeldung.com/java-util-arrays)
-- [What is [Ljava.lang.Object;?]](https://www.baeldung.com/java-tostring-array)
+- [What is \[Ljava.lang.Object;?](https://www.baeldung.com/java-tostring-array)
+- [Guide to ArrayStoreException](https://www.baeldung.com/java-arraystoreexception)
+- [Creating a Generic Array in Java](https://www.baeldung.com/java-generic-array)

core-java-modules/core-java-arrays-guides/pom.xml

@@ -17,16 +17,18 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-core.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-generator.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>3.19.0</version>
+            <scope>test</scope>
         </dependency>
     </dependencies>
-
-    <properties>
-        <jmh.version>1.19</jmh.version>
-    </properties>
 </project>

core-java-modules/core-java-arrays-guides/src/main/java/com/baeldung/array/arraystoreexception/ArrayStoreExampleCE.java

@@ -0,0 +1,11 @@
+package com.baeldung.array.arraystoreexception;
+
+public class ArrayStoreExampleCE {
+
+    public static void main(String[] args) {
+        
+        //String array[] = new String[5]; //This will lead to compile-time error at line-8 when uncommented
+        //array[0] = 2;
+    }
+
+}

core-java-modules/core-java-arrays-guides/src/main/java/com/baeldung/array/arraystoreexception/ArrayStoreExceptionExample.java

@@ -0,0 +1,16 @@
+package com.baeldung.array.arraystoreexception;
+
+public class ArrayStoreExceptionExample {
+
+    public static void main(String[] args) {
+
+        try {
+            Object array[] = new String[5];
+            array[0] = 2;
+        } catch (ArrayStoreException e) {
+            // handle the exception
+        }
+
+    }
+
+}

core-java-modules/core-java-arrays-guides/src/main/java/com/baeldung/genericarrays/MyStack.java

@@ -0,0 +1,30 @@
+package com.baeldung.genericarrays;
+
+import java.lang.reflect.Array;
+
+public class MyStack<E> {
+    private E[] elements;
+    private int size = 0;
+
+    public MyStack(Class<E> clazz, int capacity) {
+        elements = (E[]) Array.newInstance(clazz, capacity);
+    }
+
+    public void push(E item) {
+        if (size == elements.length) {
+            throw new RuntimeException();
+        }
+        elements[size++] = item;
+    }
+
+    public E pop() {
+        if (size == 0) {
+            throw new RuntimeException();
+        }
+        return elements[--size];
+    }
+
+    public E[] getAllElements() {
+        return elements;
+    }
+}

core-java-modules/core-java-arrays-guides/src/test/java/com/baeldung/genericarrays/ListToArrayUnitTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.genericarrays;
+
+import org.junit.Test;
+
+import java.util.LinkedList;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class ListToArrayUnitTest {
+
+    @Test
+    public void givenListOfItems_whenToArray_thenReturnArrayOfItems() {
+        List<String> items = new LinkedList<>();
+        items.add("first item");
+        items.add("second item");
+
+        String[] itemsAsArray = items.toArray(new String[0]);
+
+        assertEquals("first item", itemsAsArray[0]);
+        assertEquals("second item", itemsAsArray[1]);
+    }
+}

core-java-modules/core-java-arrays-guides/src/test/java/com/baeldung/genericarrays/MyStackUnitTest.java

@@ -0,0 +1,44 @@
+package com.baeldung.genericarrays;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class MyStackUnitTest {
+
+    @Test
+    public void givenStackWithTwoItems_whenPop_thenReturnLastAdded() {
+        MyStack<String> myStack = new MyStack<>(String.class, 2);
+        myStack.push("hello");
+        myStack.push("example");
+
+        assertEquals("example", myStack.pop());
+    }
+
+    @Test (expected = RuntimeException.class)
+    public void givenStackWithFixedCapacity_whenExceedCapacity_thenThrowException() {
+        MyStack<Integer> myStack = new MyStack<>(Integer.class, 2);
+        myStack.push(100);
+        myStack.push(200);
+        myStack.push(300);
+    }
+
+    @Test(expected = RuntimeException.class)
+    public void givenStack_whenPopOnEmptyStack_thenThrowException() {
+        MyStack<Integer> myStack = new MyStack<>(Integer.class, 1);
+        myStack.push(100);
+        myStack.pop();
+        myStack.pop();
+    }
+
+    @Test
+    public void givenStackWithItems_whenGetAllElements_thenSizeShouldEqualTotal() {
+        MyStack<String> myStack = new MyStack<>(String.class, 2);
+        myStack.push("hello");
+        myStack.push("example");
+
+        String[] items = myStack.getAllElements();
+
+        assertEquals(2, items.length);
+    }
+}

core-java-modules/core-java-arrays-guides/src/test/java/com/baeldung/genericarrays/StreamToArrayUnitTest.java

@@ -0,0 +1,77 @@
+package com.baeldung.genericarrays;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+import java.util.function.IntFunction;
+import java.util.stream.Stream;
+
+import static java.util.Collections.singletonList;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+public class StreamToArrayUnitTest {
+
+    @Test
+    public void givenAStream_thenCanGetArrayOfObject() {
+        Object[] strings = Stream.of("A", "AAA", "B", "AAB", "C")
+          .filter(string -> string.startsWith("A"))
+          .toArray();
+
+        assertThat(strings).containsExactly("A", "AAA", "AAB");
+        assertThat(strings).isNotInstanceOf(String[].class);
+    }
+
+    @Test
+    public void givenAStream_thenCanGetArrayOfString() {
+        String[] strings = Stream.of("A", "AAA", "B", "AAB", "C")
+          .filter(string -> string.startsWith("A"))
+          .toArray(String[]::new);
+
+        assertThat(strings).containsExactly("A", "AAA", "AAB");
+        assertThat(strings).isInstanceOf(String[].class);
+    }
+
+    @SuppressWarnings("unchecked")
+    @Test
+    public void givenAStream_whenConvertToOptional_thenCanGetArrayOfOptional() {
+        Stream<Optional<String>> stream = Stream.of("A", "AAA", "B", "AAB", "C")
+                .filter(string -> string.startsWith("A"))
+                .map(Optional::of);
+        Optional<String>[] strings = stream
+          .toArray(Optional[]::new);
+
+        assertThat(strings).containsExactly(Optional.of("A"),
+          Optional.of("AAA"),
+          Optional.of("AAB"));
+        assertThat(strings).isInstanceOf(Optional[].class);
+    }
+
+    @Test
+    public void givenAStream_whenConvertToOptional_thenCanGetArrayOfOptionalWithHelper() {
+        Optional<String>[] strings = Stream.of("A", "AAA", "B", "AAB", "C")
+          .filter(string -> string.startsWith("A"))
+          .map(Optional::of)
+          .toArray(genericArray(Optional[]::new));
+
+        assertThat(strings).containsExactly(Optional.of("A"),
+          Optional.of("AAA"),
+          Optional.of("AAB"));
+        assertThat(strings).isInstanceOf(Optional[].class);
+    }
+
+    @Test
+    public void whenInvalidUseOfGenericArray_thenIllegalCast() {
+        assertThatThrownBy(() -> {
+            ArrayList<String>[] lists = Stream.of(singletonList("A"))
+                    .toArray(genericArray(List[]::new));
+        }).isInstanceOf(ClassCastException.class);
+    }
+
+    @SuppressWarnings("unchecked")
+    private static <T, R extends T> IntFunction<R[]> genericArray(IntFunction<T[]> arrayCreator) {
+        return size -> (R[])arrayCreator.apply(size);
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/README.md

@@ -3,7 +3,9 @@
 This module contains articles about advanced operations on arrays in Java. They assume some background knowledge with arrays in Java.
 
 ### Relevant Articles: 
+
 - [How to Copy an Array in Java](https://www.baeldung.com/java-array-copy)
 - [Arrays.deepEquals](https://www.baeldung.com/java-arrays-deepequals)
 - [Find Sum and Average in a Java Array](https://www.baeldung.com/java-array-sum-average)
 - [Intersection Between two Integer Arrays](https://www.baeldung.com/java-array-intersection)
+- [Comparing Arrays in Java](https://www.baeldung.com/java-comparing-arrays)

core-java-modules/core-java-arrays-operations-advanced/pom.xml

@@ -29,8 +29,6 @@
     </dependencies>
 
     <properties>
-        <commons-lang3.version>3.9</commons-lang3.version>
-
         <assertj-core.version>3.10.0</assertj-core.version>
     </properties>
 </project>

core-java-modules/core-java-arrays-operations-advanced/src/main/java/com/baeldung/arraycompare/Plane.java

@@ -0,0 +1,39 @@
+package com.baeldung.arraycompare;
+
+import java.util.Objects;
+
+public class Plane {
+
+    private final String name;
+
+    private final String model;
+
+    public Plane(String name, String model) {
+
+        this.name = name;
+        this.model = model;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public String getModel() {
+        return model;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+        if (o == null || getClass() != o.getClass())
+            return false;
+        Plane plane = (Plane) o;
+        return Objects.equals(name, plane.name) && Objects.equals(model, plane.model);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(name, model);
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/src/main/java/com/baeldung/arrayconcat/ArrayConcatUtil.java

@@ -0,0 +1,65 @@
+package com.baeldung.arrayconcat;
+
+import java.lang.reflect.Array;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+public class ArrayConcatUtil {
+    private ArrayConcatUtil() {}
+
+    static <T> T[] concatWithCollection(T[] array1, T[] array2) {
+        List<T> resultList = new ArrayList<>(array1.length + array2.length);
+        Collections.addAll(resultList, array1);
+        Collections.addAll(resultList, array2);
+
+        @SuppressWarnings("unchecked")
+        //the type cast is safe as the array1 has the type T[]
+        T[] resultArray = (T[]) Array.newInstance(array1.getClass().getComponentType(), 0);
+        return resultList.toArray(resultArray);
+    }
+
+    static <T> T[] concatWithArrayCopy(T[] array1, T[] array2) {
+        T[] result = Arrays.copyOf(array1, array1.length + array2.length);
+        System.arraycopy(array2, 0, result, array1.length, array2.length);
+        return result;
+    }
+
+    static <T> T concatWithCopy2(T array1, T array2) {
+        if (!array1.getClass().isArray() || !array2.getClass().isArray()) {
+            throw new IllegalArgumentException("Only arrays are accepted.");
+        }
+
+        Class<?> compType1 = array1.getClass().getComponentType();
+        Class<?> compType2 = array2.getClass().getComponentType();
+
+        if (!compType1.equals(compType2)) {
+            throw new IllegalArgumentException("Two arrays have different types.");
+        }
+
+        int len1 = Array.getLength(array1);
+        int len2 = Array.getLength(array2);
+
+        @SuppressWarnings("unchecked")
+        //the cast is safe due to the previous checks
+        T result = (T) Array.newInstance(compType1, len1 + len2);
+
+        System.arraycopy(array1, 0, result, 0, len1);
+        System.arraycopy(array2, 0, result, len1, len2);
+
+        return result;
+    }
+
+    @SuppressWarnings("unchecked")
+    static <T> T[] concatWithStream(T[] array1, T[] array2) {
+        return Stream.concat(Arrays.stream(array1), Arrays.stream(array2))
+                     .toArray(size -> (T[]) Array.newInstance(array1.getClass().getComponentType(), size));
+    }
+
+    static int[] concatIntArraysWithIntStream(int[] array1, int[] array2) {
+        return IntStream.concat(Arrays.stream(array1), Arrays.stream(array2)).toArray();
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arraycompare/DeepEqualsCompareUnitTest.java

@@ -0,0 +1,30 @@
+package com.baeldung.arraycompare;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class DeepEqualsCompareUnitTest {
+
+    @Test
+    public void givenSameContents_whenDeepEquals_thenTrue() {
+        final Plane[][] planes1 = new Plane[][] { new Plane[] { new Plane("Plane 1", "A320") },
+            new Plane[] { new Plane("Plane 2", "B738") } };
+        final Plane[][] planes2 = new Plane[][] { new Plane[] { new Plane("Plane 1", "A320") },
+            new Plane[] { new Plane("Plane 2", "B738") } };
+
+        assertThat(Arrays.deepEquals(planes1, planes2)).isTrue();
+    }
+
+    @Test
+    public void givenSameContentsWithDifferentOrder_whenDeepEquals_thenFalse() {
+        final Plane[][] planes1 = new Plane[][] { new Plane[] { new Plane("Plane 1", "A320") },
+            new Plane[] { new Plane("Plane 2", "B738") } };
+        final Plane[][] planes2 = new Plane[][] { new Plane[] { new Plane("Plane 2", "B738") },
+            new Plane[] { new Plane("Plane 1", "A320") } };
+
+        assertThat(Arrays.deepEquals(planes1, planes2)).isFalse();
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arraycompare/EqualsCompareUnitTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.arraycompare;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class EqualsCompareUnitTest {
+
+    @Test
+    public void givenSameContents_whenEquals_thenTrue() {
+        final String[] planes1 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+        final String[] planes2 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+
+        assertThat(Arrays.equals(planes1, planes2)).isTrue();
+    }
+
+    @Test
+    public void givenSameContentsDifferentOrder_whenEquals_thenFalse() {
+        final String[] planes1 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+        final String[] planes2 = new String[] { "B738", "A320", "A321", "A319", "B77W", "B737", "A333", "A332" };
+
+        assertThat(Arrays.equals(planes1, planes2)).isFalse();
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arraycompare/LengthsCompareUnitTest.java

@@ -0,0 +1,18 @@
+package com.baeldung.arraycompare;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class LengthsCompareUnitTest {
+
+    @Test
+    public void givenSameContent_whenSizeCompare_thenTrue() {
+        final String[] planes1 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+        final Integer[] quantities = new Integer[] { 10, 12, 34, 45, 12, 43, 5, 2 };
+
+        assertThat(planes1).hasSize(8);
+        assertThat(quantities).hasSize(8);
+    }
+}
+

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arraycompare/OrderCompareUnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.arraycompare;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.Comparator;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.Assert.assertTrue;
+
+public class OrderCompareUnitTest {
+    @Test
+    public void givenSameContentDifferentOrder_whenSortedAndDeepEquals_thenTrue() {
+        final Plane[][] planes1 = new Plane[][] {
+            new Plane[] { new Plane("Plane 1", "A320"), new Plane("Plane 2", "B738") } };
+        final Plane[][] planes2 = new Plane[][] {
+            new Plane[] { new Plane("Plane 2", "B738"), new Plane("Plane 1", "A320") } };
+
+        Comparator<Plane> planeComparator = (o1, o2) -> {
+            if (o1.getName()
+                .equals(o2.getName())) {
+                return o2.getModel()
+                    .compareTo(o1.getModel());
+            }
+            return o2.getName()
+                .compareTo(o1.getName());
+        };
+        Arrays.sort(planes1[0], planeComparator);
+        Arrays.sort(planes2[0], planeComparator);
+
+        assertThat(Arrays.deepEquals(planes1, planes2)).isTrue();
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arraycompare/ReferenceCompareUnitTest.java

@@ -0,0 +1,30 @@
+package com.baeldung.arraycompare;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ReferenceCompareUnitTest {
+
+    @Test
+    public void givenSameReferences_whenSame_thenTrue() {
+        final String[] planes1 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+        final String[] planes2 = planes1;
+
+        assertThat(planes1).isSameAs(planes2);
+
+        planes2[0] = "747";
+
+        assertThat(planes1).isSameAs(planes2);
+        assertThat(planes2[0]).isEqualTo("747");
+        assertThat(planes1[0]).isEqualTo("747");
+    }
+
+    @Test
+    public void givenSameContentDifferentReferences_whenSame_thenFalse() {
+        final String[] planes1 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+        final String[] planes2 = new String[] { "A320", "B738", "A321", "A319", "B77W", "B737", "A333", "A332" };
+
+        assertThat(planes1).isNotSameAs(planes2);
+    }
+}

core-java-modules/core-java-arrays-operations-advanced/src/test/java/com/baeldung/arrayconcat/ArrayConcatUtilUnitTest.java

@@ -0,0 +1,99 @@
+package com.baeldung.arrayconcat;
+
+
+import com.google.common.collect.ObjectArrays;
+import com.google.common.primitives.Ints;
+import org.apache.commons.lang3.ArrayUtils;
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.fail;
+
+public class ArrayConcatUtilUnitTest {
+    private final String[] strArray1 = { "element 1", "element 2", "element 3" };
+    private final String[] strArray2 = { "element 4", "element 5" };
+    private final String[] expectedStringArray = { "element 1", "element 2", "element 3", "element 4", "element 5" };
+
+    private final int[] intArray1 = { 0, 1, 2, 3 };
+    private final int[] intArray2 = { 4, 5, 6, 7 };
+    private final int[] expectedIntArray = { 0, 1, 2, 3, 4, 5, 6, 7 };
+
+    @Test
+    public void givenTwoStringArrays_whenConcatWithList_thenGetExpectedResult() {
+        String[] result = ArrayConcatUtil.concatWithCollection(strArray1, strArray2);
+        assertThat(result).isEqualTo(expectedStringArray);
+    }
+
+    @Test
+    public void givenTwoStringArrays_whenConcatWithCopy_thenGetExpectedResult() {
+        String[] result = ArrayConcatUtil.concatWithArrayCopy(strArray1, strArray2);
+        assertThat(result).isEqualTo(expectedStringArray);
+    }
+
+    @Test
+    public void givenTwoStrings_whenConcatWithCopy2_thenGetException() {
+        String exMsg = "Only arrays are accepted.";
+        try {
+            ArrayConcatUtil.concatWithCopy2("String Nr. 1", "String Nr. 2");
+            fail(String.format("IllegalArgumentException with message:'%s' should be thrown. But it didn't", exMsg));
+        } catch (IllegalArgumentException e) {
+            assertThat(e).hasMessage(exMsg);
+        }
+    }
+
+    @Test
+    public void givenTwoArraysInDifferentTypes_whenConcatWithCopy2_thenGetException() {
+        String[] strArray = new String[] { "test 1", "test 2" };
+        Integer[] integerArray = new Integer[] { 7, 11 };
+        String exMsg = "Two arrays have different types.";
+
+        try {
+            ArrayConcatUtil.concatWithCopy2(strArray, integerArray);
+            fail(String.format("IllegalArgumentException with message:'%s' should be thrown. But it didn't", exMsg));
+        } catch (IllegalArgumentException e) {
+            assertThat(e).hasMessage(exMsg);
+        }
+    }
+
+    @Test
+    public void givenTwoArrays_whenConcatWithCopy2_thenGetExpectedResult() {
+        String[] result = ArrayConcatUtil.concatWithCopy2(strArray1, strArray2);
+        assertThat(result).isEqualTo(expectedStringArray);
+
+        int[] intResult = ArrayConcatUtil.concatWithCopy2(intArray1, intArray2);
+        assertThat(intResult).isEqualTo(expectedIntArray);
+    }
+
+    @Test
+    public void givenTwoStringArrays_whenConcatWithStream_thenGetExpectedResult() {
+        String[] result = ArrayConcatUtil.concatWithStream(strArray1, strArray2);
+        assertThat(result).isEqualTo(expectedStringArray);
+    }
+
+    @Test
+    public void givenTwoIntArrays_whenConcatWithIntStream_thenGetExpectedResult() {
+        int[] intResult = ArrayConcatUtil.concatIntArraysWithIntStream(intArray1, intArray2);
+        assertThat(intResult).isEqualTo(expectedIntArray);
+    }
+
+    @Test
+    public void givenTwoArrays_whenConcatWithCommonsLang_thenGetExpectedResult() {
+        String[] result = ArrayUtils.addAll(strArray1, strArray2);
+        assertThat(result).isEqualTo(expectedStringArray);
+
+        int[] intResult = ArrayUtils.addAll(intArray1, intArray2);
+        assertThat(intResult).isEqualTo(expectedIntArray);
+    }
+
+    @Test
+    public void givenTwoStringArrays_whenConcatWithGuava_thenGetExpectedResult() {
+        String[] result = ObjectArrays.concat(strArray1, strArray2, String.class);
+        assertThat(result).isEqualTo(expectedStringArray);
+    }
+
+    @Test
+    public void givenTwoIntArrays_whenConcatWithGuava_thenGetExpectedResult() {
+        int[] intResult = Ints.concat(intArray1, intArray2);
+        assertThat(intResult).isEqualTo(expectedIntArray);
+    }
+}

core-java-modules/core-java-arrays-operations-basic/pom.xml

@@ -24,12 +24,12 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-core.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
 
         <dependency>
@@ -68,11 +68,6 @@
 
     <properties>
         <shade.plugin.version>3.2.0</shade.plugin.version>
-
-        <commons-lang3.version>3.9</commons-lang3.version>
-
-        <jmh.version>1.19</jmh.version>
-
         <assertj-core.version>3.10.0</assertj-core.version>
     </properties>
 </project>

core-java-modules/core-java-arrays-sorting/pom.xml

@@ -31,12 +31,12 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-core.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
 
         <!-- Testing -->
@@ -76,12 +76,7 @@
 
     <properties>
         <shade.plugin.version>3.2.0</shade.plugin.version>
-
-        <commons-lang3.version>3.9</commons-lang3.version>
         <guava.version>28.2-jre</guava.version>
-
-        <jmh.version>1.19</jmh.version>
-
         <assertj-core.version>3.10.0</assertj-core.version>
     </properties>
 </project>

core-java-modules/core-java-char/README.md

@@ -0,0 +1,6 @@
+## Core Java Character
+
+This module contains articles about Java Character Class
+
+### Relevant Articles: 
+- [Character#isAlphabetic vs. Character#isLetter](https://www.baeldung.com/java-character-isletter-isalphabetic)