rebased

algorithms-miscellaneous-5/pom.xml

@@ -21,10 +21,10 @@
             <version>${commons-codec.version}</version>
         </dependency>
         <dependency>
-        <groupId>org.apache.commons</groupId>
+            <groupId>org.apache.commons</groupId>
-        <artifactId>commons-math3</artifactId>
+            <artifactId>commons-math3</artifactId>
-        <version>${commons-math3.version}</version>
+            <version>${commons-math3.version}</version>
-    </dependency>
+        </dependency>
         <dependency>
             <groupId>pl.allegro.finance</groupId>
             <artifactId>tradukisto</artifactId>

apache-cxf/README.md

@@ -3,7 +3,7 @@
 This module contains articles about Apache CXF
 
 ## Relevant Articles:
-- [Introduction to Apache CXF Aegis Data Binding](https://www.baeldung.com/aegis-data-binding-in-apache-cxf)
+
 - [Apache CXF Support for RESTful Web Services](https://www.baeldung.com/apache-cxf-rest-api)
 - [A Guide to Apache CXF with Spring](https://www.baeldung.com/apache-cxf-with-spring)
 - [Introduction to Apache CXF](https://www.baeldung.com/introduction-to-apache-cxf)

apache-cxf/cxf-aegis/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles:
+
+- [Introduction to Apache CXF Aegis Data Binding](https://www.baeldung.com/aegis-data-binding-in-apache-cxf)

apache-shiro/pom.xml

@@ -10,9 +10,9 @@
 
     <parent>
         <groupId>com.baeldung</groupId>
-        <artifactId>parent-boot-1</artifactId>
+        <artifactId>parent-boot-2</artifactId>
         <version>0.0.1-SNAPSHOT</version>
-        <relativePath>../parent-boot-1</relativePath>
+        <relativePath>../parent-boot-2</relativePath>
     </parent>
 
     <dependencies>

apache-shiro/src/main/java/com/baeldung/Main.java

@@ -1,11 +1,14 @@
 package com.baeldung;
 
 import org.apache.shiro.SecurityUtils;
-import org.apache.shiro.authc.*;
+import org.apache.shiro.authc.AuthenticationException;
+import org.apache.shiro.authc.IncorrectCredentialsException;
+import org.apache.shiro.authc.LockedAccountException;
+import org.apache.shiro.authc.UnknownAccountException;
+import org.apache.shiro.authc.UsernamePasswordToken;
 import org.apache.shiro.mgt.DefaultSecurityManager;
 import org.apache.shiro.mgt.SecurityManager;
 import org.apache.shiro.realm.Realm;
-import org.apache.shiro.realm.text.IniRealm;
 import org.apache.shiro.session.Session;
 import org.apache.shiro.subject.Subject;
 import org.slf4j.Logger;

apache-shiro/src/main/java/com/baeldung/MyCustomRealm.java

@@ -1,16 +1,24 @@
 package com.baeldung;
 
-import org.apache.shiro.authc.*;
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+import org.apache.shiro.authc.AuthenticationException;
+import org.apache.shiro.authc.AuthenticationInfo;
+import org.apache.shiro.authc.AuthenticationToken;
+import org.apache.shiro.authc.SimpleAuthenticationInfo;
+import org.apache.shiro.authc.UnknownAccountException;
+import org.apache.shiro.authc.UsernamePasswordToken;
 import org.apache.shiro.authz.AuthorizationInfo;
 import org.apache.shiro.authz.SimpleAuthorizationInfo;
 import org.apache.shiro.realm.jdbc.JdbcRealm;
 import org.apache.shiro.subject.PrincipalCollection;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-import java.sql.Connection;
-import java.sql.SQLException;
-import java.util.*;
 
 public class MyCustomRealm extends JdbcRealm {
 

apache-shiro/src/main/java/com/baeldung/shiro/permissions/custom/Main.java

@@ -1,14 +1,15 @@
 package com.baeldung.shiro.permissions.custom;
 
-import com.baeldung.MyCustomRealm;
 import org.apache.shiro.SecurityUtils;
-import org.apache.shiro.authc.*;
+import org.apache.shiro.authc.AuthenticationException;
+import org.apache.shiro.authc.IncorrectCredentialsException;
+import org.apache.shiro.authc.LockedAccountException;
+import org.apache.shiro.authc.UnknownAccountException;
+import org.apache.shiro.authc.UsernamePasswordToken;
 import org.apache.shiro.config.Ini;
 import org.apache.shiro.mgt.DefaultSecurityManager;
 import org.apache.shiro.mgt.SecurityManager;
-import org.apache.shiro.realm.Realm;
 import org.apache.shiro.realm.text.IniRealm;
-import org.apache.shiro.session.Session;
 import org.apache.shiro.subject.Subject;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

atomikos/README.md

@@ -1,7 +1,6 @@
 ## Atomikos
-
 This module contains articles about Atomikos
 
 ### Relevant Articles: 
 
-- [Guide Transactions Using Atomikos]()
+- [A Guide to Atomikos](https://www.baeldung.com/java-atomikos)

aws-app-sync/pom.xml

@@ -0,0 +1,56 @@
+<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-starter-parent</artifactId>
+        <version>2.2.6.RELEASE</version>
+        <relativePath/> <!-- lookup parent from repository -->
+    </parent>
+
+    <groupId>com.baeldung</groupId>
+    <artifactId>aws-app-sync</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>aws-app-sync</name>
+
+    <description>Spring Boot using AWS App Sync</description>
+
+    <properties>
+        <java.version>1.8</java.version>
+    </properties>
+
+    <dependencies>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+            <exclusions>
+                <exclusion>
+                    <groupId>org.junit.vintage</groupId>
+                    <artifactId>junit-vintage-engine</artifactId>
+                </exclusion>
+            </exclusions>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-webflux</artifactId>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

aws-app-sync/src/main/java/com/baeldung/awsappsync/AppSyncClientHelper.java

@@ -0,0 +1,32 @@
+package com.baeldung.awsappsync;
+
+import org.springframework.http.HttpMethod;
+import org.springframework.http.MediaType;
+import org.springframework.web.reactive.function.BodyInserters;
+import org.springframework.web.reactive.function.client.WebClient;
+
+import java.nio.charset.StandardCharsets;
+import java.util.Map;
+
+public class AppSyncClientHelper {
+
+    static String apiUrl = "<INSERT API URL HERE>";
+    static String apiKey = "<INSERT API KEY HERE>";
+    static String API_KEY_HEADER = "x-api-key";
+
+    public static WebClient.ResponseSpec getResponseBodySpec(Map<String, Object> requestBody) {
+        return WebClient
+                .builder()
+                .baseUrl(apiUrl)
+                .defaultHeader(API_KEY_HEADER, apiKey)
+                .defaultHeader("Content-Type", "application/json")
+                .build()
+                .method(HttpMethod.POST)
+                .uri("/graphql")
+                .body(BodyInserters.fromValue(requestBody))
+                .accept(MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML)
+                .acceptCharset(StandardCharsets.UTF_8)
+                .retrieve();
+    }
+
+}

aws-app-sync/src/main/java/com/baeldung/awsappsync/AwsAppSyncApplication.java

@@ -0,0 +1,13 @@
+package com.baeldung.awsappsync;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class AwsAppSyncApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(AwsAppSyncApplication.class, args);
+    }
+
+}

aws-app-sync/src/test/java/com/baeldung/awsappsync/AwsAppSyncApplicationTests.java

@@ -0,0 +1,74 @@
+package com.baeldung.awsappsync;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.web.reactive.function.client.WebClient;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+@SpringBootTest
+@Disabled
+class AwsAppSyncApplicationTests {
+
+    @Test
+    void givenGraphQuery_whenListEvents_thenReturnAllEvents() {
+
+        Map<String, Object> requestBody = new HashMap<>();
+        requestBody.put("query", "query ListEvents {"
+                + "  listEvents {"
+                + "    items {"
+                + "      id"
+                + "      name"
+                + "      where"
+                + "      when"
+                + "      description"
+                + "    }"
+                + "  }"
+                + "}");
+        requestBody.put("variables", "");
+        requestBody.put("operationName", "ListEvents");
+
+        String bodyString = AppSyncClientHelper.getResponseBodySpec(requestBody)
+                .bodyToMono(String.class).block();
+
+        assertNotNull(bodyString);
+        assertTrue(bodyString.contains("My First Event"));
+        assertTrue(bodyString.contains("where"));
+        assertTrue(bodyString.contains("when"));
+    }
+
+    @Test
+    void givenGraphAdd_whenMutation_thenReturnIdNameDesc() {
+
+        String queryString = "mutation add {"
+                + "    createEvent("
+                + "        name:\"My added GraphQL event\""
+                + "        where:\"Day 2\""
+                + "        when:\"Saturday night\""
+                + "        description:\"Studying GraphQL\""
+                + "    ){"
+                + "        id"
+                + "        name"
+                + "        description"
+                + "    }"
+                + "}";
+
+        Map<String, Object> requestBody = new HashMap<>();
+        requestBody.put("query", queryString);
+        requestBody.put("variables", "");
+        requestBody.put("operationName", "add");
+
+        WebClient.ResponseSpec response = AppSyncClientHelper.getResponseBodySpec(requestBody);
+
+        String bodyString = response.bodyToMono(String.class).block();
+
+        assertNotNull(bodyString);
+        assertTrue(bodyString.contains("My added GraphQL event"));
+        assertFalse(bodyString.contains("where"));
+        assertFalse(bodyString.contains("when"));
+    }
+}

bazel/bazelapp/README.md

@@ -1,3 +0,0 @@
-### Relevant Articles:
-
-- [Building Java Applications with Bazel](https://www.baeldung.com/bazel-build-tool)

cas/cas-secured-app/pom.xml

@@ -16,10 +16,6 @@
         <relativePath>../../parent-boot-2</relativePath>
     </parent>
 
-    <properties>
-        <spring-boot.version>2.2.6.RELEASE</spring-boot.version>
-    </properties>
-
     <dependencies>
         <dependency>
             <groupId>org.springframework.boot</groupId>

core-groovy-2/README.md

@@ -13,4 +13,5 @@ This module contains articles about core Groovy concepts
 - [Metaprogramming in Groovy](https://www.baeldung.com/groovy-metaprogramming)
 - [A Quick Guide to Working with Web Services in Groovy](https://www.baeldung.com/groovy-web-services)
 - [Categories in Groovy](https://www.baeldung.com/groovy-categories)
+- [How to Determine the Data Type in Groovy](https://www.baeldung.com/groovy-determine-data-type)
 - [[<-- Prev]](/core-groovy)

core-groovy/README.md

@@ -12,4 +12,5 @@ This module contains articles about core Groovy concepts
 - [Closures in Groovy](https://www.baeldung.com/groovy-closures)
 - [Converting a String to a Date in Groovy](https://www.baeldung.com/groovy-string-to-date)
 - [Guide to I/O in Groovy](https://www.baeldung.com/groovy-io)
+- [Convert String to Integer in Groovy](https://www.baeldung.com/groovy-convert-string-to-integer)
 - [[More -->]](/core-groovy-2)

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

@@ -8,3 +8,4 @@ This module contains articles about Java 14.
 - [Java Text Blocks](https://www.baeldung.com/java-text-blocks)
 - [Pattern Matching for instanceof in Java 14](https://www.baeldung.com/java-pattern-matching-instanceof)
 - [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)

core-java-modules/core-java-14/src/main/java/com/baeldung/java14/record/Person.java

@@ -0,0 +1,22 @@
+package com.baeldung.java14.record;
+
+import java.util.Objects;
+
+public record Person (String name, String address) {
+	
+	public static String UNKWOWN_ADDRESS = "Unknown";
+	public static String UNNAMED = "Unnamed";
+
+	public Person {
+		Objects.requireNonNull(name);
+		Objects.requireNonNull(address);
+	}
+	
+	public Person(String name) {
+		this(name, UNKWOWN_ADDRESS);
+	}
+	
+	public static Person unnamed(String address) {
+		return new Person(UNNAMED, address);
+	}
+}

core-java-modules/core-java-14/src/test/java/com/baeldung/java14/foreign/api/ForeignMemoryUnitTest.java

@@ -0,0 +1,84 @@
+package com.baeldung.java14.foreign.api;
+
+import jdk.incubator.foreign.*;
+import org.junit.Test;
+
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThat;
+
+import java.lang.invoke.VarHandle;
+import java.nio.ByteOrder;
+
+public class ForeignMemoryUnitTest {
+
+    @Test
+    public void whenAValueIsSet_thenAccessTheValue() {
+        long value = 10;
+        MemoryAddress memoryAddress =
+          MemorySegment.allocateNative(8).baseAddress();
+        VarHandle varHandle = MemoryHandles.varHandle(long.class,
+          ByteOrder.nativeOrder());
+        varHandle.set(memoryAddress, value);
+        assertThat(varHandle.get(memoryAddress), is(value));
+    }
+
+    @Test
+    public void whenMultipleValuesAreSet_thenAccessAll() {
+        VarHandle varHandle = MemoryHandles.varHandle(int.class,
+          ByteOrder.nativeOrder());
+
+        try(MemorySegment memorySegment =
+          MemorySegment.allocateNative(100)) {
+            MemoryAddress base = memorySegment.baseAddress();
+            for(int i=0; i<25; i++) {
+                varHandle.set(base.addOffset((i*4)), i);
+            }
+            for(int i=0; i<25; i++) {
+                assertThat(varHandle.get(base.addOffset((i*4))), is(i));
+            }
+        }
+    }
+
+    @Test
+    public void whenSetValuesWithMemoryLayout_thenTheyCanBeRetrieved() {
+        SequenceLayout sequenceLayout =
+          MemoryLayout.ofSequence(25,
+            MemoryLayout.ofValueBits(64, ByteOrder.nativeOrder()));
+        VarHandle varHandle =
+          sequenceLayout.varHandle(long.class,
+            MemoryLayout.PathElement.sequenceElement());
+
+        try(MemorySegment memorySegment =
+          MemorySegment.allocateNative(sequenceLayout)) {
+            MemoryAddress base = memorySegment.baseAddress();
+            for(long i=0; i<sequenceLayout.elementCount().getAsLong(); i++) {
+                varHandle.set(base, i, i);
+            }
+            for(long i=0; i<sequenceLayout.elementCount().getAsLong(); i++) {
+                assertThat(varHandle.get(base, i), is(i));
+            }
+        }
+    }
+
+    @Test
+    public void whenSlicingMemorySegment_thenTheyCanBeAccessedIndividually() {
+        MemoryAddress memoryAddress =
+          MemorySegment.allocateNative(12).baseAddress();
+        MemoryAddress memoryAddress1 =
+          memoryAddress.segment().asSlice(0,4).baseAddress();
+        MemoryAddress memoryAddress2 =
+          memoryAddress.segment().asSlice(4,4).baseAddress();
+        MemoryAddress memoryAddress3 =
+          memoryAddress.segment().asSlice(8,4).baseAddress();
+
+        VarHandle intHandle =
+          MemoryHandles.varHandle(int.class, ByteOrder.nativeOrder());
+        intHandle.set(memoryAddress1, Integer.MIN_VALUE);
+        intHandle.set(memoryAddress2, 0);
+        intHandle.set(memoryAddress3, Integer.MAX_VALUE);
+
+        assertThat(intHandle.get(memoryAddress1), is(Integer.MIN_VALUE));
+        assertThat(intHandle.get(memoryAddress2), is(0));
+        assertThat(intHandle.get(memoryAddress3), is(Integer.MAX_VALUE));
+    }
+}

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

@@ -0,0 +1,150 @@
+package com.baeldung.java14.record;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class PersonTest {
+
+    @Test
+    public void givenSameNameAndAddress_whenEquals_thenPersonsEqual() {
+
+        String name = "John Doe";
+        String address = "100 Linda Ln.";
+
+        Person person1 = new Person(name, address);
+        Person person2 = new Person(name, address);
+
+        assertTrue(person1.equals(person2));
+    }
+    
+    @Test
+    public void givenDifferentObject_whenEquals_thenNotEqual() {
+
+        Person person = new Person("John Doe", "100 Linda Ln.");
+
+        assertFalse(person.equals(new Object()));
+    }
+
+    @Test
+    public void givenDifferentName_whenEquals_thenPersonsNotEqual() {
+    
+        String address = "100 Linda Ln.";
+    
+        Person person1 = new Person("Jane Doe", address);
+        Person person2 = new Person("John Doe", address);
+    
+        assertFalse(person1.equals(person2));
+    }
+    
+    @Test
+    public void givenDifferentAddress_whenEquals_thenPersonsNotEqual() {
+    
+        String name = "John Doe";
+    
+        Person person1 = new Person(name, "100 Linda Ln.");
+        Person person2 = new Person(name, "200 London Ave.");
+    
+        assertFalse(person1.equals(person2));
+    }
+
+    @Test
+    public void givenSameNameAndAddress_whenHashCode_thenPersonsEqual() {
+
+        String name = "John Doe";
+        String address = "100 Linda Ln.";
+
+        Person person1 = new Person(name, address);
+        Person person2 = new Person(name, address);
+
+        assertEquals(person1.hashCode(), person2.hashCode());
+    }
+    
+    @Test
+    public void givenDifferentObject_whenHashCode_thenNotEqual() {
+
+        Person person = new Person("John Doe", "100 Linda Ln.");
+
+        assertNotEquals(person.hashCode(), new Object().hashCode());
+    }
+
+    @Test
+    public void givenDifferentName_whenHashCode_thenPersonsNotEqual() {
+
+        String address = "100 Linda Ln.";
+
+        Person person1 = new Person("Jane Doe", address);
+        Person person2 = new Person("John Doe", address);
+
+        assertNotEquals(person1.hashCode(), person2.hashCode());
+    }
+
+    @Test
+    public void givenDifferentAddress_whenHashCode_thenPersonsNotEqual() {
+
+        String name = "John Doe";
+
+        Person person1 = new Person(name, "100 Linda Ln.");
+        Person person2 = new Person(name, "200 London Ave.");
+
+        assertNotEquals(person1.hashCode(), person2.hashCode());
+    }
+
+    @Test
+    public void givenValidNameAndAddress_whenGetNameAndAddress_thenExpectedValuesReturned() {
+
+        String name = "John Doe";
+        String address = "100 Linda Ln.";
+
+        Person person = new Person(name, address);
+
+        assertEquals(name, person.name());
+        assertEquals(address, person.address());
+    }
+
+    @Test
+    public void givenValidNameAndAddress_whenToString_thenCorrectStringReturned() {
+
+        String name = "John Doe";
+        String address = "100 Linda Ln.";
+
+        Person person = new Person(name, address);
+
+        assertEquals("Person[name=" + name + ", address=" + address + "]", person.toString());
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void givenNullName_whenConstruct_thenErrorThrown() {
+        new Person(null, "100 Linda Ln.");
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void givenNullAddress_whenConstruct_thenErrorThrown() {
+        new Person("John Doe", null);
+    }
+
+    @Test
+    public void givenUnknownAddress_whenConstructing_thenAddressPopulated() {
+
+        String name = "John Doe";
+
+        Person person = new Person(name);
+
+        assertEquals(name, person.name());
+        assertEquals(Person.UNKWOWN_ADDRESS, person.address());
+    }
+
+    @Test
+    public void givenUnnamed_whenConstructingThroughFactory_thenNamePopulated() {
+
+        String address = "100 Linda Ln.";
+
+        Person person = Person.unnamed(address);
+
+        assertEquals(Person.UNNAMED, person.name());
+        assertEquals(address, person.address());
+    }
+}

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

@@ -9,3 +9,4 @@ This module contains articles about the improvements to core Java features intro
 - [Java 9 Stream API Improvements](https://www.baeldung.com/java-9-stream-api)
 - [Java 9 java.util.Objects Additions](https://www.baeldung.com/java-9-objects-new)
 - [Java 9 CompletableFuture API Improvements](https://www.baeldung.com/java-9-completablefuture)
+- [Java InputStream to Byte Array and ByteBuffer](https://www.baeldung.com/convert-input-stream-to-array-of-bytes)

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

@@ -33,6 +33,11 @@
             <artifactId>guava</artifactId>
             <version>${guava.version}</version>
         </dependency>
+        <dependency>
+            <groupId>commons-io</groupId>
+            <artifactId>commons-io</artifactId>
+            <version>${commons-io.version}</version>
+        </dependency>
         <dependency>
             <groupId>org.junit.platform</groupId>
             <artifactId>junit-platform-runner</artifactId>

core-java-modules/core-java-9-improvements/src/test/java/com/baeldung/java9/io/conversion/InputStreamToByteArrayUnitTest.java

@@ -0,0 +1,57 @@
+package com.baeldung.java9.io.conversion;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+
+import org.apache.commons.io.IOUtils;
+import org.junit.Test;
+
+import com.google.common.io.ByteSource;
+import com.google.common.io.ByteStreams;
+
+public class InputStreamToByteArrayUnitTest {
+
+    @Test
+    public final void givenUsingPlainJavaOnFixedSizeStream_whenConvertingAnInputStreamToAByteArray_thenCorrect() throws IOException {
+        final InputStream initialStream = new ByteArrayInputStream(new byte[] { 0, 1, 2 });
+        final byte[] targetArray = new byte[initialStream.available()];
+        initialStream.read(targetArray);
+    }
+
+    @Test
+    public final void givenUsingPlainJavaOnUnknownSizeStream_whenConvertingAnInputStreamToAByteArray_thenCorrect() throws IOException {
+        final InputStream is = new ByteArrayInputStream(new byte[] { 0, 1, 2 });
+
+        final ByteArrayOutputStream buffer = new ByteArrayOutputStream();
+        int nRead;
+        final byte[] data = new byte[1024];
+        while ((nRead = is.read(data, 0, data.length)) != -1) {
+            buffer.write(data, 0, nRead);
+        }
+
+        buffer.flush();
+        final byte[] byteArray = buffer.toByteArray();
+    }
+
+    @Test
+    public void givenUsingPlainJava9_whenConvertingAnInputStreamToAByteArray_thenCorrect() throws IOException {
+        final InputStream is = new ByteArrayInputStream(new byte[] { 0, 1, 2 });
+
+        byte[] data = is.readAllBytes();
+    }
+
+    @Test
+    public final void givenUsingGuava_whenConvertingAnInputStreamToAByteArray_thenCorrect() throws IOException {
+        final InputStream initialStream = ByteSource.wrap(new byte[] { 0, 1, 2 })
+            .openStream();
+        final byte[] targetArray = ByteStreams.toByteArray(initialStream);
+    }
+
+    @Test
+    public final void givenUsingCommonsIO_whenConvertingAnInputStreamToAByteArray_thenCorrect() throws IOException {
+        final InputStream initialStream = new ByteArrayInputStream(new byte[] { 0, 1, 2 });
+        final byte[] targetArray = IOUtils.toByteArray(initialStream);
+    }
+}

core-java-modules/core-java-9-improvements/src/test/java/com/baeldung/java9/io/conversion/InputStreamToByteBufferUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.inputstreamtobytes;
+package com.baeldung.java9.io.conversion;
 
 import com.google.common.io.ByteSource;
 import com.google.common.io.ByteStreams;

core-java-modules/core-java-collections-maps-3/README.md

@@ -5,4 +5,5 @@ This module contains articles about Map data structures in Java.
 ### Relevant Articles: 
 - [Java TreeMap vs HashMap](https://www.baeldung.com/java-treemap-vs-hashmap)
 - [Comparing Two HashMaps in Java](https://www.baeldung.com/java-compare-hashmaps)
+- [The Map.computeIfAbsent() Method](https://www.baeldung.com/java-map-computeifabsent)
 - More articles: [[<-- prev]](/core-java-modules/core-java-collections-maps-2)

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

@@ -4,5 +4,5 @@
 
 ### Relevant Articles: 
 - [Using a Mutex Object in Java](https://www.baeldung.com/java-mutex)
-- [Testing Multi-Threaded Code in Java] (https://www.baeldung.com/java-testing-multithreaded)
+- [Testing Multi-Threaded Code in Java](https://www.baeldung.com/java-testing-multithreaded)
 

core-java-modules/core-java-concurrency-advanced-3/README.md

@@ -11,4 +11,5 @@ This module contains articles about advanced topics about multithreading with co
 - [Guide to Work Stealing in Java](https://www.baeldung.com/java-work-stealing)
 - [Asynchronous Programming in Java](https://www.baeldung.com/java-asynchronous-programming)
 - [Java Thread Deadlock and Livelock](https://www.baeldung.com/java-deadlock-livelock)
+- [Guide to AtomicStampedReference in Java](https://www.baeldung.com/java-atomicstampedreference)
 - [[<-- previous]](/core-java-modules/core-java-concurrency-advanced-2)

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/lockfree/NonBlockingQueue.java

@@ -0,0 +1,81 @@
+package com.baeldung.lockfree;
+
+import java.util.NoSuchElementException;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+
+public class NonBlockingQueue<T> {
+
+    private final AtomicReference<Node<T>> head, tail;
+    private final AtomicInteger size;
+
+    public NonBlockingQueue() {
+        head = new AtomicReference<>(null);
+        tail = new AtomicReference<>(null);
+        size = new AtomicInteger();
+        size.set(0);
+    }
+
+    public void add(T element) {
+        if (element == null) {
+            throw new NullPointerException();
+        }
+
+        Node<T> node = new Node<>(element);
+        Node<T> currentTail;
+        do {
+            currentTail = tail.get();
+            node.setPrevious(currentTail);
+        } while(!tail.compareAndSet(currentTail, node));
+
+        if(node.previous != null) {
+            node.previous.next = node;
+        }
+
+        head.compareAndSet(null, node); //if we are inserting the first element
+        size.incrementAndGet();
+    }
+
+    public T get() {
+        if(head.get() == null) {
+            throw new NoSuchElementException();
+        }
+
+        Node<T> currentHead;
+        Node<T> nextNode;
+        do {
+            currentHead = head.get();
+            nextNode = currentHead.getNext();
+        } while(!head.compareAndSet(currentHead, nextNode));
+
+        size.decrementAndGet();
+        return currentHead.getValue();
+    }
+
+    public int size() {
+        return this.size.get();
+    }
+
+    private class Node<T> {
+        private final T value;
+        private volatile Node<T> next;
+        private volatile Node<T> previous;
+
+        public Node(T value) {
+            this.value = value;
+            this.next = null;
+        }
+
+        public T getValue() {
+            return value;
+        }
+
+        public Node<T> getNext() {
+            return next;
+        }
+
+        public void setPrevious(Node<T> previous) {
+            this.previous = previous;
+        }
+    }
+}

core-java-modules/core-java-concurrency-advanced-3/src/test/java/com/baeldung/exchanger/ExchangerPipeLineManualTest.java

@@ -0,0 +1,83 @@
+package com.baeldung.exchanger;
+
+import java.util.Queue;
+import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.Exchanger;
+import java.util.concurrent.ExecutionException;
+import org.junit.Test;
+
+import static java.util.concurrent.CompletableFuture.runAsync;
+
+
+
+public class ExchangerPipeLineManualTest {
+
+    private static final int BUFFER_SIZE = 100;
+
+    @Test
+    public void givenData_whenPassedThrough_thenCorrect() throws InterruptedException, ExecutionException {
+
+        Exchanger<Queue<String>> readerExchanger = new Exchanger<>();
+        Exchanger<Queue<String>> writerExchanger = new Exchanger<>();
+        int counter = 0;
+
+        Runnable reader = () -> {
+            Queue<String> readerBuffer = new ConcurrentLinkedQueue<>();
+            while (true) {
+                readerBuffer.add(UUID.randomUUID().toString());
+                if (readerBuffer.size() >= BUFFER_SIZE) {
+                    try {
+                        readerBuffer = readerExchanger.exchange(readerBuffer);
+                    } catch (InterruptedException e) {
+                        Thread.currentThread().interrupt();
+                        throw new RuntimeException(e);
+                    }
+                }
+            }
+        };
+
+        Runnable processor = () -> {
+            Queue<String> processorBuffer = new ConcurrentLinkedQueue<>();
+            Queue<String> writerBuffer = new ConcurrentLinkedQueue<>();
+            try {
+                processorBuffer = readerExchanger.exchange(processorBuffer);
+                while (true) {
+                    writerBuffer.add(processorBuffer.poll());
+                    if (processorBuffer.isEmpty()) {
+                        try {
+                            processorBuffer = readerExchanger.exchange(processorBuffer);
+                            writerBuffer = writerExchanger.exchange(writerBuffer);
+                        } catch (InterruptedException e) {
+                            Thread.currentThread().interrupt();
+                            throw new RuntimeException(e);
+                        }
+                    }
+                }
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                throw new RuntimeException(e);
+            }
+        };
+
+        Runnable writer = () -> {
+            Queue<String> writerBuffer = new ConcurrentLinkedQueue<>();
+            try {
+                writerBuffer = writerExchanger.exchange(writerBuffer);
+                while (true) {
+                    System.out.println(writerBuffer.poll());
+                    if (writerBuffer.isEmpty()) {
+                        writerBuffer = writerExchanger.exchange(writerBuffer);
+                    }
+                }
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                throw new RuntimeException(e);
+            }
+        };
+
+        CompletableFuture.allOf(runAsync(reader), runAsync(processor), runAsync(writer)).get();
+    }
+
+}

core-java-modules/core-java-concurrency-advanced-3/src/test/java/com/baeldung/exchanger/ExchangerUnitTest.java

@@ -0,0 +1,63 @@
+package com.baeldung.exchanger;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Exchanger;
+
+import java.util.concurrent.ExecutionException;
+import org.junit.Test;
+
+import static java.util.concurrent.CompletableFuture.runAsync;
+
+public class ExchangerUnitTest {
+    
+    
+    @Test
+    public void givenThreads_whenMessageExchanged_thenCorrect() {
+        Exchanger<String> exchanger = new Exchanger<>();
+
+        Runnable taskA = () -> {
+            try {
+                String message = exchanger.exchange("from A");
+                assertEquals("from B", message);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                throw new RuntimeException(e);
+            }
+        };
+
+        Runnable taskB = () -> {
+            try {
+                String message = exchanger.exchange("from B");
+                assertEquals("from A", message);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                throw new RuntimeException(e);
+            }
+        };
+
+        CompletableFuture.allOf(runAsync(taskA), runAsync(taskB)).join();
+    }
+
+    @Test
+    public void givenThread_WhenExchangedMessage_thenCorrect() throws InterruptedException, ExecutionException {
+        Exchanger<String> exchanger = new Exchanger<>();
+
+        Runnable runner = () -> {
+            try {
+                String message = exchanger.exchange("from runner");
+                assertEquals("to runner", message);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+                throw new RuntimeException(e);
+            }
+        };
+
+        CompletableFuture<Void> result = CompletableFuture.runAsync(runner);
+        String msg = exchanger.exchange("to runner");
+        assertEquals("from runner", msg);
+        result.join();
+    }
+
+}

core-java-modules/core-java-concurrency-collections-2/pom.xml

@@ -23,7 +23,12 @@
             <artifactId>jmh-generator-annprocess</artifactId>
             <version>${jmh.version}</version>
         </dependency>
-
+		<dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
     <build>
         <sourceDirectory>src</sourceDirectory>
@@ -42,6 +47,8 @@
     <properties>
         <jmh.version>1.21</jmh.version>
         <guava.version>28.2-jre</guava.version>
+         <!-- testing -->
+        <assertj.version>3.6.1</assertj.version>
     </properties>
 
 </project>

core-java-modules/core-java-concurrency-collections-2/src/test/java/com/baeldung/concurrent/queue/TestConcurrentLinkedQueue.java

@@ -0,0 +1,66 @@
+package com.baeldung.concurrent.queue;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertThat;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+
+import org.junit.FixMethodOrder;
+import org.junit.Test;
+
+@FixMethodOrder
+public class TestConcurrentLinkedQueue {
+
+    @Test
+    public void givenThereIsExistingCollection_WhenAddedIntoQueue_ThenShouldContainElements() {
+        Collection<Integer> elements = Arrays.asList(1, 2, 3, 4, 5);
+        ConcurrentLinkedQueue<Integer> concurrentLinkedQueue = new ConcurrentLinkedQueue<>(elements);
+        assertThat(concurrentLinkedQueue).containsExactly(1, 2, 3, 4, 5);
+    }
+
+    @Test
+    public void givenQueueIsEmpty_WhenAccessingTheQueue_ThenQueueReturnsNull() throws InterruptedException {
+        ExecutorService executorService = Executors.newFixedThreadPool(1);
+        ConcurrentLinkedQueue<Integer> concurrentLinkedQueue = new ConcurrentLinkedQueue<>();
+        executorService.submit(() -> assertNull("Retrieve object is null", concurrentLinkedQueue.poll()));
+        TimeUnit.SECONDS.sleep(1);
+        executorService.awaitTermination(1, TimeUnit.SECONDS);
+        executorService.shutdown();
+    }
+
+    @Test
+    public void givenProducerOffersElementInQueue_WhenConsumerPollsQueue_ThenItRetrievesElement() throws Exception {
+        int element = 1;
+
+        ExecutorService executorService = Executors.newFixedThreadPool(2);
+        ConcurrentLinkedQueue<Integer> concurrentLinkedQueue = new ConcurrentLinkedQueue<>();
+        Runnable offerTask = () -> concurrentLinkedQueue.offer(element);
+
+        Callable<Integer> pollTask = () -> {
+            while (concurrentLinkedQueue.peek() != null) {
+                return concurrentLinkedQueue.poll()
+                    .intValue();
+            }
+            return null;
+        };
+
+        executorService.submit(offerTask);
+        TimeUnit.SECONDS.sleep(1);
+
+        Future<Integer> returnedElement = executorService.submit(pollTask);
+        assertThat(returnedElement.get()
+            .intValue(), is(equalTo(element)));
+        executorService.awaitTermination(1, TimeUnit.SECONDS);
+        executorService.shutdown();
+    }
+}

core-java-modules/core-java-concurrency-collections-2/src/test/java/com/baeldung/concurrent/queue/TestLinkedBlockingQueue.java

@@ -0,0 +1,81 @@
+package com.baeldung.concurrent.queue;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.TimeUnit;
+
+import org.junit.FixMethodOrder;
+import org.junit.Test;
+
+@FixMethodOrder
+public class TestLinkedBlockingQueue {
+
+    @Test
+    public void givenThereIsExistingCollection_WhenAddedIntoQueue_ThenShouldContainElements() {
+        Collection<Integer> elements = Arrays.asList(1, 2, 3, 4, 5);
+        LinkedBlockingQueue<Integer> linkedBlockingQueue = new LinkedBlockingQueue<>(elements);
+        assertThat(linkedBlockingQueue).containsExactly(1, 2, 3, 4, 5);
+    }
+
+    @Test
+    public void givenQueueIsEmpty_WhenAccessingTheQueue_ThenThreadBlocks() throws InterruptedException {
+        ExecutorService executorService = Executors.newFixedThreadPool(1);
+        LinkedBlockingQueue<Integer> linkedBlockingQueue = new LinkedBlockingQueue<>();
+        executorService.submit(() -> {
+            try {
+                linkedBlockingQueue.take();
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+        });
+        TimeUnit.SECONDS.sleep(1);
+        executorService.awaitTermination(1, TimeUnit.SECONDS);
+        executorService.shutdown();
+    }
+
+    @Test
+    public void givenProducerPutsElementInQueue_WhenConsumerAccessQueue_ThenItRetrieve() {
+        int element = 10;
+        ExecutorService executorService = Executors.newFixedThreadPool(2);
+        LinkedBlockingQueue<Integer> linkedBlockingQueue = new LinkedBlockingQueue<>();
+        Runnable putTask = () -> {
+            try {
+                linkedBlockingQueue.put(element);
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+        };
+
+        Callable<Integer> takeTask = () -> {
+            try {
+                return linkedBlockingQueue.take();
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+            return null;
+        };
+
+        executorService.submit(putTask);
+        Future<Integer> returnElement = executorService.submit(takeTask);
+        try {
+            TimeUnit.SECONDS.sleep(1);
+            assertThat(returnElement.get()
+                .intValue(), is(equalTo(element)));
+            executorService.awaitTermination(1, TimeUnit.SECONDS);
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+
+        executorService.shutdown();
+    }
+}

core-java-modules/core-java-date-operations-2/src/main/java/com/baeldung/weeknumber/WeekNumberUsingCalendar.java

@@ -0,0 +1,41 @@
+package com.baeldung.weeknumber;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.Calendar;
+import java.util.Date;
+import java.util.Locale;
+
+public class WeekNumberUsingCalendar {
+
+    public int getWeekNumberFrom(String day, String dateFormat, Locale locale) throws ParseException {
+        SimpleDateFormat sdf = new SimpleDateFormat(dateFormat);
+
+        Calendar calendar = Calendar.getInstance(locale);
+        Date date = sdf.parse(day);
+        calendar.setTime(date);
+
+        return calendar.get(Calendar.WEEK_OF_YEAR);
+    }
+
+    public int getWeekNumberFrom(int year, int month, int day, Locale locale) {
+        Calendar calendar = Calendar.getInstance(locale);
+        calendar.set(year, month, day);
+
+        return calendar.get(Calendar.WEEK_OF_YEAR);
+    }
+
+    public int getWeekNumberFrom(int year, int month, int day, int firstDayOfWeek, int minimalDaysInFirstWeek, Locale locale) {
+        Calendar calendar = Calendar.getInstance(locale);
+        calendar.setFirstDayOfWeek(firstDayOfWeek);
+        calendar.setMinimalDaysInFirstWeek(minimalDaysInFirstWeek);
+        calendar.set(year, month, day);
+
+        return calendar.get(Calendar.WEEK_OF_YEAR);
+    }
+
+    public static void main(String[] args) {
+        WeekNumberUsingCalendar calendar = new WeekNumberUsingCalendar();
+        System.out.println(calendar.getWeekNumberFrom(2020, 2, 22, Locale.CANADA));
+    }
+}

core-java-modules/core-java-date-operations-2/src/main/java/com/baeldung/weeknumber/WeekNumberUsingLocalDate.java

@@ -0,0 +1,30 @@
+package com.baeldung.weeknumber;
+
+import java.time.LocalDate;
+import java.time.format.DateTimeFormatter;
+import java.time.temporal.ChronoField;
+import java.time.temporal.WeekFields;
+import java.util.Locale;
+
+public class WeekNumberUsingLocalDate {
+
+    public Integer getWeekNumberUsingWeekFiedsFrom(String day, String dayFormat, Locale locale) {
+        LocalDate date = LocalDate.parse(day, DateTimeFormatter.ofPattern(dayFormat));
+
+        return date.get(WeekFields.of(locale)
+            .weekOfYear());
+    }
+
+    public Integer getWeekNumberUsinWeekFieldsFrom(int year, int month, int day, Locale locale) {
+        LocalDate date = LocalDate.of(year, month, day);
+
+        return date.get(WeekFields.of(locale)
+            .weekOfYear());
+    }
+
+    public Integer getWeekNumberUsingChronoFieldFrom(int year, int month, int day) {
+        LocalDate date = LocalDate.of(year, month, day);
+
+        return date.get(ChronoField.ALIGNED_WEEK_OF_YEAR);
+    }
+}

core-java-modules/core-java-date-operations-2/src/test/java/com/baeldung/weeknumber/WeekNumberUsingCalendarUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.weeknumber;
+
+import static org.junit.Assert.assertEquals;
+
+import java.text.ParseException;
+import java.util.Calendar;
+import java.util.Locale;
+
+import org.junit.Test;
+
+public class WeekNumberUsingCalendarUnitTest {
+    @Test
+    public void givenDateInStringAndDateFormatUsingLocaleItaly_thenGettingWeekNumberUsingCalendarIsCorrectlyReturned() throws ParseException {
+        WeekNumberUsingCalendar calendar = new WeekNumberUsingCalendar();
+
+        assertEquals(12, calendar.getWeekNumberFrom("20200322", "yyyyMMdd", Locale.ITALY));
+    }
+
+    @Test
+    public void givenDateInStringAndDateFormatUsingLocaleCanada_thenGettingWeekNumberUsingCalendarIsCorrectlyReturned() throws ParseException {
+        WeekNumberUsingCalendar calendar = new WeekNumberUsingCalendar();
+
+        assertEquals(13, calendar.getWeekNumberFrom("20200322", "yyyyMMdd", Locale.CANADA));
+    }
+
+    @Test
+    public void givenDateInYearMonthDayNumbersLocaleItaly_thenGettingWeekNumberUsingCalendarIsCorrectlyReturned() {
+        WeekNumberUsingCalendar calendar = new WeekNumberUsingCalendar();
+
+        assertEquals(12, calendar.getWeekNumberFrom(2020, 2, 22, Locale.ITALY));
+    }
+
+    @Test
+    public void givenDateInYearMonthDayNumbersLocaleItalyChangingWeekCalculationSettings_thenGettingWeekNumberUsingCalendarIsCorrectlyReturned() {
+        WeekNumberUsingCalendar calendar = new WeekNumberUsingCalendar();
+
+        assertEquals(13, calendar.getWeekNumberFrom(2020, 2, 22, Calendar.SUNDAY, 4, Locale.ITALY));
+    }
+
+    @Test
+    public void givenDateInYearMonthDayNumbersLocaleCanada_thenGettingWeekNumberUsingCalendarIsCorrectlyReturned() {
+        WeekNumberUsingCalendar calendar = new WeekNumberUsingCalendar();
+
+        assertEquals(13, calendar.getWeekNumberFrom(2020, 2, 22, Locale.CANADA));
+    }
+}

core-java-modules/core-java-date-operations-2/src/test/java/com/baeldung/weeknumber/WeekNumberUsingLocalDateUnitTest.java

@@ -0,0 +1,49 @@
+package com.baeldung.weeknumber;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Locale;
+
+import org.junit.Test;
+
+public class WeekNumberUsingLocalDateUnitTest {
+    @Test
+    public void givenDateInStringAndDateFormatUsingWeekFieldsWithLocaleItaly_thenGettingWeekNumberUsingLocalDateIsCorrectlyReturned() {
+        WeekNumberUsingLocalDate localDate = new WeekNumberUsingLocalDate();
+
+        assertEquals(12, localDate.getWeekNumberUsingWeekFiedsFrom("20200322", "yyyyMMdd", Locale.ITALY)
+            .longValue());
+    }
+
+    @Test
+    public void givenDateInStringAndDateFormatUsingWeekFieldsWithLocaleCanada_thenGettingWeekNumberUsingLocalDateIsCorrectlyReturned() {
+        WeekNumberUsingLocalDate localDate = new WeekNumberUsingLocalDate();
+
+        assertEquals(13, localDate.getWeekNumberUsingWeekFiedsFrom("20200322", "yyyyMMdd", Locale.CANADA)
+            .longValue());
+    }
+
+    @Test
+    public void givenDateInStringAndDateFormatUsingChronoFieds_thenGettingWeekNumberUsingLocalDateIsCorrectlyReturned() {
+        WeekNumberUsingLocalDate localDate = new WeekNumberUsingLocalDate();
+
+        assertEquals(12, localDate.getWeekNumberUsingChronoFieldFrom(2020, 3, 22)
+            .longValue());
+    }
+
+    @Test
+    public void givenDateInYearMonthDayNumbersUsingWeekFieldsWithLocaleItaly_thenGettingWeekNumberUsingLocalDateIsCorrectlyReturned() {
+        WeekNumberUsingLocalDate localDate = new WeekNumberUsingLocalDate();
+
+        assertEquals(12, localDate.getWeekNumberUsinWeekFieldsFrom(2020, 3, 22, Locale.ITALY)
+            .longValue());
+    }
+
+    @Test
+    public void givenDateInYearMonthDayNumbersUsingWeekFieldsWithLocaleCanada_thenGettingWeekNumberUsingLocalDateIsCorrectlyReturned() {
+        WeekNumberUsingLocalDate localDate = new WeekNumberUsingLocalDate();
+
+        assertEquals(13, localDate.getWeekNumberUsinWeekFieldsFrom(2020, 3, 22, Locale.CANADA)
+            .longValue());
+    }
+}

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

@@ -9,3 +9,6 @@ This module contains articles about core java exceptions
 - [java.net.UnknownHostException: Invalid Hostname for Server](https://www.baeldung.com/java-unknownhostexception)
 - [How to Handle Java SocketException](https://www.baeldung.com/java-socketexception)
 - [Java Suppressed Exceptions](https://www.baeldung.com/java-suppressed-exceptions)
+- [Java – Try with Resources](https://www.baeldung.com/java-try-with-resources)
+- [Java Global Exception Handler](https://www.baeldung.com/java-global-exception-handler)
+- [How to Find an Exception’s Root Cause in Java](https://www.baeldung.com/java-exception-root-cause)

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

@@ -23,6 +23,11 @@
             <version>${assertj-core.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons.lang3.version}</version>
+        </dependency>
     </dependencies>
 
     <description> </description>
@@ -30,6 +35,7 @@
 
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <commons.lang3.version>3.10</commons.lang3.version>
         <!-- testing -->
         <assertj-core.version>3.10.0</assertj-core.version>
     </properties>

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/Arithmetic.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/ArrayIndexOutOfBounds.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/ClassCast.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/FileNotFound.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import java.io.BufferedReader;
 import java.io.File;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/GlobalExceptionHandler.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/IllegalArgument.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/IllegalState.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import java.util.ArrayList;
 import java.util.Iterator;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/InterruptedExceptionExample.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/MalformedURL.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import java.net.MalformedURLException;
 import java.net.URL;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/NullPointer.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/NumberFormat.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/ParseExceptionExample.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import java.text.DateFormat;
 import java.text.ParseException;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/globalexceptionhandler/StringIndexOutOfBounds.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

core-java-modules/core-java-exceptions-2/src/main/java/com/baeldung/rootcausefinder/RootCauseFinder.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.rootcausefinder;
+package com.baeldung.rootcausefinder;
 
 import java.time.LocalDate;
 import java.time.Period;

core-java-modules/core-java-exceptions-2/src/test/java/com/baeldung/globalexceptionhandler/GlobalExceptionHandlerUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.exceptions.globalexceptionhandler;
+package com.baeldung.globalexceptionhandler;
 
 import org.junit.After;
 import org.junit.Before;

core-java-modules/core-java-exceptions-2/src/test/java/com/baeldung/rootcausefinder/RootCauseFinderUnitTest.java

@@ -1,7 +1,7 @@
-package com.baeldung.exceptions.rootcausefinder;
+package com.baeldung.rootcausefinder;
 
-import com.baeldung.exceptions.rootcausefinder.RootCauseFinder.CalculationException;
+import com.baeldung.rootcausefinder.RootCauseFinder.CalculationException;
-import com.baeldung.exceptions.rootcausefinder.RootCauseFinder.DateOutOfRangeException;
+import com.baeldung.rootcausefinder.RootCauseFinder.DateOutOfRangeException;
 import com.google.common.base.Throwables;
 import org.apache.commons.lang3.exception.ExceptionUtils;
 import org.junit.jupiter.api.Assertions;
@@ -11,8 +11,7 @@ import java.time.LocalDate;
 import java.time.format.DateTimeParseException;
 import java.time.temporal.ChronoUnit;
 
-import static com.baeldung.exceptions.rootcausefinder.RootCauseFinder.AgeCalculator;
+import static com.baeldung.rootcausefinder.RootCauseFinder.AgeCalculator;
-import static com.baeldung.exceptions.rootcausefinder.RootCauseFinder.findCauseUsingPlainJava;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /**
@@ -38,7 +37,7 @@ public class RootCauseFinderUnitTest {
         try {
             AgeCalculator.calculateAge("010102");
         } catch (CalculationException ex) {
-            assertTrue(findCauseUsingPlainJava(ex) instanceof DateTimeParseException);
+            assertTrue(RootCauseFinder.findCauseUsingPlainJava(ex) instanceof DateTimeParseException);
         }
     }
 
@@ -47,7 +46,7 @@ public class RootCauseFinderUnitTest {
         try {
             AgeCalculator.calculateAge("2020-04-04");
         } catch (CalculationException ex) {
-            assertTrue(findCauseUsingPlainJava(ex) instanceof DateOutOfRangeException);
+            assertTrue(RootCauseFinder.findCauseUsingPlainJava(ex) instanceof DateOutOfRangeException);
         }
     }
 
@@ -56,7 +55,7 @@ public class RootCauseFinderUnitTest {
         try {
             AgeCalculator.calculateAge(null);
         } catch (Exception ex) {
-            assertTrue(findCauseUsingPlainJava(ex) instanceof IllegalArgumentException);
+            assertTrue(RootCauseFinder.findCauseUsingPlainJava(ex) instanceof IllegalArgumentException);
         }
     }
 

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

@@ -12,9 +12,5 @@ This module contains articles about core java exceptions
 - [“Sneaky Throws” in Java](https://www.baeldung.com/java-sneaky-throws)
 - [The StackOverflowError in Java](https://www.baeldung.com/java-stack-overflow-error)
 - [Checked and Unchecked Exceptions in Java](https://www.baeldung.com/java-checked-unchecked-exceptions)
-- [Java – Try with Resources](https://www.baeldung.com/java-try-with-resources)
-- [Java Global Exception Handler](https://www.baeldung.com/java-global-exception-handler)
 - [Common Java Exceptions](https://www.baeldung.com/java-common-exceptions)
-- [How to Find an Exception’s Root Cause in Java](https://www.baeldung.com/java-exception-root-cause)
-- [Is It a Bad Practice to Catch Throwable?](https://www.baeldung.com/java-catch-throwable-bad-practice)
 - [[Next -->]](/core-java-modules/core-java-exceptions-2)

core-java-modules/core-java-io-conversions-2/README.md

@@ -4,6 +4,5 @@ This module contains articles about core Java input/output(IO) conversions.
 
 ### Relevant Articles:
 - [Java InputStream to String](https://www.baeldung.com/convert-input-stream-to-string)
-- [Java InputStream to Byte Array and ByteBuffer](https://www.baeldung.com/convert-input-stream-to-array-of-bytes)
 - [Java – Write an InputStream to a File](https://www.baeldung.com/convert-input-stream-to-a-file)
 - More articles: [[<-- prev]](/core-java-modules/core-java-io-conversions)

core-java-modules/core-java-io-conversions-2/src/test/java/com/baeldung/inputstreamtostring/JavaInputStreamToXUnitTest.java

@@ -2,7 +2,6 @@ package com.baeldung.inputstreamtostring;
 
 import com.google.common.base.Charsets;
 import com.google.common.io.ByteSource;
-import com.google.common.io.ByteStreams;
 import com.google.common.io.CharStreams;
 import com.google.common.io.Files;
 import org.apache.commons.io.FileUtils;
@@ -11,13 +10,26 @@ import org.junit.Test;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.io.*;
+import java.io.BufferedReader;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.OutputStream;
+import java.io.Reader;
+import java.io.StringReader;
+import java.io.StringWriter;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
 import java.util.Scanner;
 import java.util.UUID;
+import java.util.stream.Collectors;
 
 import static org.apache.commons.lang3.RandomStringUtils.randomAlphabetic;
 import static org.hamcrest.Matchers.equalTo;
@@ -46,6 +58,18 @@ public class JavaInputStreamToXUnitTest {
         assertEquals(textBuilder.toString(), originalString);
     }
 
+    @Test
+    public void givenUsingJava8_whenConvertingAnInputStreamToAString_thenCorrect() {
+        final String originalString = randomAlphabetic(DEFAULT_SIZE);
+        final InputStream inputStream = new ByteArrayInputStream(originalString.getBytes());
+
+        final String text = new BufferedReader(new InputStreamReader(inputStream, Charset.forName(StandardCharsets.UTF_8.name())))
+          .lines()
+          .collect(Collectors.joining("\n"));
+
+        assertThat(text, equalTo(originalString));
+    }
+
     @Test
     public final void givenUsingJava7_whenConvertingAnInputStreamToAString_thenCorrect() throws IOException {
         final String originalString = randomAlphabetic(DEFAULT_SIZE);
@@ -127,42 +151,6 @@ public class JavaInputStreamToXUnitTest {
         assertThat(result, equalTo(originalString));
     }
 
-    // tests - InputStream to byte[]
-
-    @Test
-    public final void givenUsingPlainJavaOnFixedSizeStream_whenConvertingAnInputStreamToAByteArray_thenCorrect() throws IOException {
-        final InputStream initialStream = new ByteArrayInputStream(new byte[] { 0, 1, 2 });
-        final byte[] targetArray = new byte[initialStream.available()];
-        initialStream.read(targetArray);
-    }
-
-    @Test
-    public final void givenUsingPlainJavaOnUnknownSizeStream_whenConvertingAnInputStreamToAByteArray_thenCorrect() throws IOException {
-        final InputStream is = new ByteArrayInputStream(new byte[] { 0, 1, 2 });
-
-        final ByteArrayOutputStream buffer = new ByteArrayOutputStream();
-        int nRead;
-        final byte[] data = new byte[1024];
-        while ((nRead = is.read(data, 0, data.length)) != -1) {
-            buffer.write(data, 0, nRead);
-        }
-
-        buffer.flush();
-        final byte[] byteArray = buffer.toByteArray();
-    }
-
-    @Test
-    public final void givenUsingGuava_whenConvertingAnInputStreamToAByteArray_thenCorrect() throws IOException {
-        final InputStream initialStream = ByteSource.wrap(new byte[] { 0, 1, 2 }).openStream();
-        final byte[] targetArray = ByteStreams.toByteArray(initialStream);
-    }
-
-    @Test
-    public final void givenUsingCommonsIO_whenConvertingAnInputStreamToAByteArray_thenCorrect() throws IOException {
-        final InputStream initialStream = new ByteArrayInputStream(new byte[] { 0, 1, 2 });
-        final byte[] targetArray = IOUtils.toByteArray(initialStream);
-    }
-
     // tests - InputStream to File
 
     @Test

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

@@ -20,7 +20,12 @@
         <dependency>
             <groupId>org.apache.commons</groupId>
             <artifactId>commons-lang3</artifactId>
-            <version>3.9</version>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
         </dependency>
         <dependency>
             <groupId>commons-beanutils</groupId>
@@ -65,6 +70,8 @@
         <jmh-generator.version>1.19</jmh-generator.version>
         <assertj.version>3.12.2</assertj.version>
         <commons.beanutils.version>1.9.4</commons.beanutils.version>
+        <commons-lang3.version>3.10</commons-lang3.version>
+        <guava.version>29.0-jre</guava.version>
     </properties>
 
 </project>

core-java-modules/core-java-lang-2/src/main/java/com/baeldung/comparing/PersonWithEquals.java

@@ -0,0 +1,51 @@
+package com.baeldung.comparing;
+
+import java.time.LocalDate;
+import java.util.Objects;
+
+public class PersonWithEquals {
+    private String firstName;
+    private String lastName;
+    private LocalDate birthDate;
+
+    public PersonWithEquals(String firstName, String lastName) {
+        if (firstName == null || lastName == null) {
+            throw new NullPointerException("Names can't be null");
+        }
+        this.firstName = firstName;
+        this.lastName = lastName;
+    }
+
+    public PersonWithEquals(String firstName, String lastName, LocalDate birthDate) {
+        this(firstName, lastName);
+
+        this.birthDate = birthDate;
+    }
+
+    public String firstName() {
+        return firstName;
+    }
+
+    public String lastName() {
+        return lastName;
+    }
+
+    public LocalDate birthDate() {
+        return birthDate;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        PersonWithEquals that = (PersonWithEquals) o;
+        return firstName.equals(that.firstName) &&
+          lastName.equals(that.lastName) &&
+          Objects.equals(birthDate, that.birthDate);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(firstName, lastName);
+    }
+}

core-java-modules/core-java-lang-2/src/main/java/com/baeldung/comparing/PersonWithEqualsAndComparable.java

@@ -0,0 +1,62 @@
+package com.baeldung.comparing;
+
+import java.time.LocalDate;
+import java.util.Objects;
+
+public class PersonWithEqualsAndComparable implements Comparable<PersonWithEqualsAndComparable> {
+    private String firstName;
+    private String lastName;
+    private LocalDate birthDate;
+
+    public PersonWithEqualsAndComparable(String firstName, String lastName) {
+        if (firstName == null || lastName == null) {
+            throw new NullPointerException("Names can't be null");
+        }
+        this.firstName = firstName;
+        this.lastName = lastName;
+    }
+
+    public PersonWithEqualsAndComparable(String firstName, String lastName, LocalDate birthDate) {
+        this(firstName, lastName);
+
+        this.birthDate = birthDate;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        PersonWithEqualsAndComparable that = (PersonWithEqualsAndComparable) o;
+        return firstName.equals(that.firstName) &&
+          lastName.equals(that.lastName) &&
+          Objects.equals(birthDate, that.birthDate);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(firstName, lastName);
+    }
+
+    @Override
+    public int compareTo(PersonWithEqualsAndComparable o) {
+        int lastNamesComparison = this.lastName.compareTo(o.lastName);
+        if (lastNamesComparison == 0) {
+            int firstNamesComparison = this.firstName.compareTo(o.firstName);
+            if (firstNamesComparison == 0) {
+                if (this.birthDate != null && o.birthDate != null) {
+                    return this.birthDate.compareTo(o.birthDate);
+                } else if (this.birthDate != null) {
+                  return 1;
+                } else if (o.birthDate != null) {
+                    return -1;
+                } else {
+                    return 0;
+                }
+            } else {
+                return firstNamesComparison;
+            }
+        } else {
+            return lastNamesComparison;
+        }
+    }
+}

core-java-modules/core-java-lang-2/src/main/java/com/baeldung/comparing/PersonWithEqualsAndComparableUsingComparator.java

@@ -0,0 +1,60 @@
+package com.baeldung.comparing;
+
+import java.time.LocalDate;
+import java.util.Comparator;
+import java.util.Objects;
+
+public class PersonWithEqualsAndComparableUsingComparator implements Comparable<PersonWithEqualsAndComparableUsingComparator> {
+    private String firstName;
+    private String lastName;
+    private LocalDate birthDate;
+
+    public PersonWithEqualsAndComparableUsingComparator(String firstName, String lastName) {
+        if (firstName == null || lastName == null) {
+            throw new NullPointerException("Names can't be null");
+        }
+        this.firstName = firstName;
+        this.lastName = lastName;
+    }
+
+    public PersonWithEqualsAndComparableUsingComparator(String firstName, String lastName, LocalDate birthDate) {
+        this(firstName, lastName);
+
+        this.birthDate = birthDate;
+    }
+
+    public String firstName() {
+        return firstName;
+    }
+
+    public String lastName() {
+        return lastName;
+    }
+
+    public LocalDate birthDate() {
+        return birthDate;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        PersonWithEqualsAndComparableUsingComparator that = (PersonWithEqualsAndComparableUsingComparator) o;
+        return firstName.equals(that.firstName) &&
+          lastName.equals(that.lastName) &&
+          Objects.equals(birthDate, that.birthDate);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(firstName, lastName);
+    }
+
+    @Override
+    public int compareTo(PersonWithEqualsAndComparableUsingComparator o) {
+        return Comparator.comparing(PersonWithEqualsAndComparableUsingComparator::lastName)
+          .thenComparing(PersonWithEqualsAndComparableUsingComparator::firstName)
+          .thenComparing(PersonWithEqualsAndComparableUsingComparator::birthDate, Comparator.nullsLast(Comparator.naturalOrder()))
+          .compare(this, o);
+    }
+}

core-java-modules/core-java-lang-2/src/main/java/com/baeldung/comparing/PersonWithEqualsAndWrongComparable.java

@@ -0,0 +1,44 @@
+package com.baeldung.comparing;
+
+import java.time.LocalDate;
+import java.util.Objects;
+
+public class PersonWithEqualsAndWrongComparable implements Comparable<PersonWithEqualsAndWrongComparable> {
+    private String firstName;
+    private String lastName;
+    private LocalDate birthDate;
+
+    public PersonWithEqualsAndWrongComparable(String firstName, String lastName) {
+        if (firstName == null || lastName == null) {
+            throw new NullPointerException("Names can't be null");
+        }
+        this.firstName = firstName;
+        this.lastName = lastName;
+    }
+
+    public PersonWithEqualsAndWrongComparable(String firstName, String lastName, LocalDate birthDate) {
+        this(firstName, lastName);
+
+        this.birthDate = birthDate;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        PersonWithEqualsAndWrongComparable that = (PersonWithEqualsAndWrongComparable) o;
+        return firstName.equals(that.firstName) &&
+          lastName.equals(that.lastName) &&
+          Objects.equals(birthDate, that.birthDate);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(firstName, lastName);
+    }
+
+    @Override
+    public int compareTo(PersonWithEqualsAndWrongComparable o) {
+        return this.lastName.compareTo(o.lastName);
+    }
+}

core-java-modules/core-java-lang-2/src/main/java/com/baeldung/comparing/PersonWithoutEquals.java

@@ -0,0 +1,11 @@
+package com.baeldung.comparing;
+
+public class PersonWithoutEquals {
+    private String firstName;
+    private String lastName;
+
+    public PersonWithoutEquals(String firstName, String lastName) {
+        this.firstName = firstName;
+        this.lastName = lastName;
+    }
+}

core-java-modules/core-java-lang-2/src/test/java/com/baeldung/comparing/ApacheCommonsObjectUtilsUnitTest.java

@@ -0,0 +1,59 @@
+package com.baeldung.comparing;
+
+import org.apache.commons.lang3.ObjectUtils;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class ApacheCommonsObjectUtilsUnitTest {
+
+    @Test
+    void givenTwoStringsWithSameValues_whenApacheCommonsEqualityMethods_thenEqualsTrueNotEqualsFalse() {
+        String a = new String("Hello!");
+        String b = new String("Hello!");
+
+        assertThat(ObjectUtils.equals(a, b)).isTrue();
+        assertThat(ObjectUtils.notEqual(a, b)).isFalse();
+    }
+
+    @Test
+    void givenTwoStringsWithDifferentValues_whenApacheCommonsEqualityMethods_thenEqualsFalseNotEqualsTrue() {
+        String a = new String("Hello!");
+        String b = new String("Hello World!");
+
+        assertThat(ObjectUtils.equals(a, b)).isFalse();
+        assertThat(ObjectUtils.notEqual(a, b)).isTrue();
+    }
+
+    @Test
+    void givenTwoStringsWithConsecutiveValues_whenApacheCommonsCompare_thenNegative() {
+        String first = new String("Hello!");
+        String second = new String("How are you?");
+
+        assertThat(ObjectUtils.compare(first, second)).isNegative();
+    }
+
+    @Test
+    void givenTwoStringsWithSameValues_whenApacheCommonsEqualityMethods_thenEqualsFalseNotEqualsTrue() {
+        String first = new String("Hello!");
+        String second = new String("Hello!");
+
+        assertThat(ObjectUtils.compare(first, second)).isZero();
+    }
+
+    @Test
+    void givenTwoStringsWithConsecutiveValues_whenApacheCommonsCompareReversed_thenPositive() {
+        String first = new String("Hello!");
+        String second = new String("How are you?");
+
+        assertThat(ObjectUtils.compare(second, first)).isPositive();
+    }
+
+    @Test
+    void givenTwoStringsOneNull_whenApacheCommonsCompare_thenPositive() {
+        String first = new String("Hello!");
+        String second = null;
+
+        assertThat(ObjectUtils.compare(first, second, false)).isPositive();
+    }
+}

core-java-modules/core-java-lang-2/src/test/java/com/baeldung/comparing/ComparableInterfaceUnitTest.java

@@ -0,0 +1,107 @@
+package com.baeldung.comparing;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.SortedSet;
+import java.util.TreeSet;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class ComparableInterfaceUnitTest {
+
+    @Test
+    void givenTwoConsecutiveStrings_whenCompareTo_thenNegative() {
+        String first = "Google";
+        String second = "Microsoft";
+
+        assertThat(first.compareTo(second)).isNegative();
+    }
+
+    @Test
+    void givenTwoEqualsStrings_whenCompareTo_thenZero() {
+        String first = "Google";
+        String second = "Google";
+
+        assertThat(first.compareTo(second)).isZero();
+    }
+
+    @Test
+    void givenTwoConsecutiveStrings_whenReversedCompareTo_thenPositive() {
+        String first = "Google";
+        String second = "Microsoft";
+
+        assertThat(second.compareTo(first)).isPositive();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsAndWrongComparableAndConsecutiveLastNames_whenCompareTo_thenNegative() {
+        PersonWithEqualsAndWrongComparable richard = new PersonWithEqualsAndWrongComparable("Richard", "Jefferson");
+        PersonWithEqualsAndWrongComparable joe = new PersonWithEqualsAndWrongComparable("Joe", "Portman");
+
+        assertThat(richard.compareTo(joe)).isNegative();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsAndWrongComparableAndSameLastNames_whenReversedCompareTo_thenZero() {
+        PersonWithEqualsAndWrongComparable richard = new PersonWithEqualsAndWrongComparable("Richard", "Jefferson");
+        PersonWithEqualsAndWrongComparable mike = new PersonWithEqualsAndWrongComparable("Mike", "Jefferson");
+
+        assertThat(richard.compareTo(mike)).isZero();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsAndWrongComparableAndConsecutiveLastNames_whenReversedCompareTo_thenPositive() {
+        PersonWithEqualsAndWrongComparable richard = new PersonWithEqualsAndWrongComparable("Richard", "Jefferson");
+        PersonWithEqualsAndWrongComparable joe = new PersonWithEqualsAndWrongComparable("Joe", "Portman");
+
+        assertThat(joe.compareTo(richard)).isPositive();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsAndWrongComparableAndSameLastNames_whenSortedSet_thenProblem() {
+        PersonWithEqualsAndWrongComparable richard = new PersonWithEqualsAndWrongComparable("Richard", "Jefferson");
+        PersonWithEqualsAndWrongComparable mike = new PersonWithEqualsAndWrongComparable("Mike", "Jefferson");
+
+        SortedSet<PersonWithEqualsAndWrongComparable> people = new TreeSet<>();
+        people.add(richard);
+        people.add(mike);
+
+        assertThat(people).containsExactly(richard);
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsAndComparableAndConsecutiveLastNames_whenCompareTo_thenNegative() {
+        PersonWithEqualsAndComparable richard = new PersonWithEqualsAndComparable("Richard", "Jefferson");
+        PersonWithEqualsAndComparable joe = new PersonWithEqualsAndComparable("Joe", "Portman");
+
+        assertThat(richard.compareTo(joe)).isNegative();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsAndComparableAndSameLastNames_whenReversedCompareTo_thenZero() {
+        PersonWithEqualsAndComparable richard = new PersonWithEqualsAndComparable("Richard", "Jefferson");
+        PersonWithEqualsAndComparable mike = new PersonWithEqualsAndComparable("Mike", "Jefferson");
+
+        assertThat(richard.compareTo(mike)).isPositive();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsAndComparableAndConsecutiveLastNames_whenReversedCompareTo_thenPositive() {
+        PersonWithEqualsAndComparable richard = new PersonWithEqualsAndComparable("Richard", "Jefferson");
+        PersonWithEqualsAndComparable joe = new PersonWithEqualsAndComparable("Joe", "Portman");
+
+        assertThat(joe.compareTo(richard)).isPositive();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsAndComparableAndSameLastNames_whenSortedSet_thenProblem() {
+        PersonWithEqualsAndComparable richard = new PersonWithEqualsAndComparable("Richard", "Jefferson");
+        PersonWithEqualsAndComparable mike = new PersonWithEqualsAndComparable("Mike", "Jefferson");
+
+        SortedSet<PersonWithEqualsAndComparable> people = new TreeSet<>();
+        people.add(richard);
+        people.add(mike);
+
+        assertThat(people).containsExactly(mike, richard);
+    }
+}

core-java-modules/core-java-lang-2/src/test/java/com/baeldung/comparing/ComparatorInterfaceUnitTest.java

@@ -0,0 +1,81 @@
+package com.baeldung.comparing;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.*;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class ComparatorInterfaceUnitTest {
+
+    @Test
+    void givenListOfTwoPersonWithEqualsAndComparatorByFirstName_whenSort_thenSortedByFirstNames() {
+        PersonWithEquals joe = new PersonWithEquals("Joe", "Portman");
+        PersonWithEquals allan = new PersonWithEquals("Allan", "Dale");
+
+        List<PersonWithEquals> people = new ArrayList<>();
+        people.add(joe);
+        people.add(allan);
+
+        Comparator<PersonWithEquals> compareByFirstNames = new Comparator<PersonWithEquals>() {
+            @Override
+            public int compare(PersonWithEquals o1, PersonWithEquals o2) {
+                return o1.firstName().compareTo(o2.firstName());
+            }
+        };
+        people.sort(compareByFirstNames);
+
+        assertThat(people).containsExactly(allan, joe);
+    }
+
+    @Test
+    void givenListOfTwoPersonWithEqualsAndComparatorByFirstNameFunctionalStyle_whenSort_thenSortedByFirstNames() {
+        PersonWithEquals joe = new PersonWithEquals("Joe", "Portman");
+        PersonWithEquals allan = new PersonWithEquals("Allan", "Dale");
+
+        List<PersonWithEquals> people = new ArrayList<>();
+        people.add(joe);
+        people.add(allan);
+
+        Comparator<PersonWithEquals> compareByFirstNames = Comparator.comparing(PersonWithEquals::firstName);
+        people.sort(compareByFirstNames);
+
+        assertThat(people).containsExactly(allan, joe);
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsAndComparableUsingComparatorAndConsecutiveLastNames_whenCompareTo_thenNegative() {
+        PersonWithEqualsAndComparableUsingComparator richard = new PersonWithEqualsAndComparableUsingComparator("Richard", "Jefferson");
+        PersonWithEqualsAndComparableUsingComparator joe = new PersonWithEqualsAndComparableUsingComparator("Joe", "Portman");
+
+        assertThat(richard.compareTo(joe)).isNegative();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsAndComparableUsingComparatorAndSameLastNames_whenReversedCompareTo_thenZero() {
+        PersonWithEqualsAndComparableUsingComparator richard = new PersonWithEqualsAndComparableUsingComparator("Richard", "Jefferson");
+        PersonWithEqualsAndComparableUsingComparator mike = new PersonWithEqualsAndComparableUsingComparator("Mike", "Jefferson");
+
+        assertThat(richard.compareTo(mike)).isPositive();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsAndComparableUsingComparatorAndConsecutiveLastNames_whenReversedCompareTo_thenPositive() {
+        PersonWithEqualsAndComparableUsingComparator richard = new PersonWithEqualsAndComparableUsingComparator("Richard", "Jefferson");
+        PersonWithEqualsAndComparableUsingComparator joe = new PersonWithEqualsAndComparableUsingComparator("Joe", "Portman");
+
+        assertThat(joe.compareTo(richard)).isPositive();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsAndComparableUsingComparatorAndSameLastNames_whenSortedSet_thenProblem() {
+        PersonWithEqualsAndComparableUsingComparator richard = new PersonWithEqualsAndComparableUsingComparator("Richard", "Jefferson");
+        PersonWithEqualsAndComparableUsingComparator mike = new PersonWithEqualsAndComparableUsingComparator("Mike", "Jefferson");
+
+        SortedSet<PersonWithEqualsAndComparableUsingComparator> people = new TreeSet<>();
+        people.add(richard);
+        people.add(mike);
+
+        assertThat(people).containsExactly(mike, richard);
+    }
+}

core-java-modules/core-java-lang-2/src/test/java/com/baeldung/comparing/EqualityOperatorUnitTest.java

@@ -0,0 +1,116 @@
+package com.baeldung.comparing;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class EqualityOperatorUnitTest {
+
+    @Test
+    void givenTwoIntsWithSameValues_whenEqualityOperators_thenConsideredSame() {
+        int a = 1;
+        int b = 1;
+
+        assertThat(a == b).isTrue();
+        assertThat(a != b).isFalse();
+    }
+
+    @Test
+    void givenTwoIntsWithDifferentValues_whenEqualityOperators_thenNotConsideredSame() {
+        int a = 1;
+        int b = 2;
+
+        assertThat(a == b).isFalse();
+        assertThat(a != b).isTrue();
+    }
+
+    @Test
+    void givenTwoIntsWithSameValuesOneWrapped_whenEqualityOperators_thenConsideredSame() {
+        int a = 1;
+        Integer b = new Integer(1);
+
+        assertThat(a == b).isTrue();
+        assertThat(a != b).isFalse();
+    }
+
+    @Test
+    void givenTwoIntsWithDifferentValuesOneWrapped_whenEqualityOperators_thenNotConsideredSame() {
+        int a = 1;
+        Integer b = new Integer(2);
+
+        assertThat(a == b).isFalse();
+        assertThat(a != b).isTrue();
+    }
+
+    @Test
+    void givenTwoIntegersWithSameValues_whenEqualityOperators_thenNotConsideredSame() {
+        Integer a = new Integer(1);
+        Integer b = new Integer(1);
+
+        assertThat(a == b).isFalse();
+        assertThat(a != b).isTrue();
+    }
+
+    @Test
+    void givenTwoIntegersWithDifferentValues_whenEqualityOperators_thenNotConsideredSame() {
+        Integer a = new Integer(1);
+        Integer b = new Integer(2);
+
+        assertThat(a == b).isFalse();
+        assertThat(a != b).isTrue();
+    }
+
+    @Test
+    void givenTwoIntegersWithSameReference_whenEqualityOperators_thenConsideredSame() {
+        Integer a = new Integer(1);
+        Integer b = a;
+
+        assertThat(a == b).isTrue();
+        assertThat(a != b).isFalse();
+    }
+
+    @Test
+    void givenTwoIntegersFromValueOfWithSameValues_whenEqualityOperators_thenConsideredSame() {
+        Integer a = Integer.valueOf(1);
+        Integer b = Integer.valueOf(1);
+
+        assertThat(a == b).isTrue();
+        assertThat(a != b).isFalse();
+    }
+
+    @Test
+    void givenTwoStringsWithSameValues_whenEqualityOperators_thenNotConsideredSame() {
+        String a = new String("Hello!");
+        String b = new String("Hello!");
+
+        assertThat(a == b).isFalse();
+        assertThat(a != b).isTrue();
+    }
+
+    @Test
+    void givenTwoStringsFromLiteralsWithSameValues_whenEqualityOperators_thenConsideredSame() {
+        String a = "Hello!";
+        String b = "Hello!";
+
+        assertThat(a == b).isTrue();
+        assertThat(a != b).isFalse();
+    }
+
+    @Test
+    void givenTwoNullObjects_whenEqualityOperators_thenConsideredSame() {
+        Object a = null;
+        Object b = null;
+
+        assertThat(a == b).isTrue();
+        assertThat(a != b).isFalse();
+    }
+
+    @Test
+    void givenTwoObjectsOneNull_whenEqualityOperators_thenNotConsideredSame() {
+        Object a = null;
+        Object b = "Hello!";
+
+        assertThat(a == b).isFalse();
+        assertThat(a != b).isTrue();
+    }
+}

core-java-modules/core-java-lang-2/src/test/java/com/baeldung/comparing/EqualsMethodUnitTest.java

@@ -0,0 +1,73 @@
+package com.baeldung.comparing;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class EqualsMethodUnitTest {
+
+    @Test
+    void givenTwoIntegersWithSameValue_whenEquals_thenTrue() {
+        Integer a = new Integer(1);
+        Integer b = new Integer(1);
+
+        assertThat(a.equals(b)).isTrue();
+    }
+
+    @Test
+    void givenTwoStringsWithSameValue_whenEquals_thenTrue() {
+        String a = new String("Hello!");
+        String b = new String("Hello!");
+
+        assertThat(a.equals(b)).isTrue();
+    }
+
+    @Test
+    void givenTwoStringsWithDifferentValue_whenEquals_thenFalse() {
+        String a = new String("Hello!");
+        String b = new String("Hello World!");
+
+        assertThat(a.equals(b)).isFalse();
+    }
+
+    @Test
+    void givenTwoObjectsFirstNull_whenEquals_thenNullPointerExceptionThrown() {
+        Object a = null;
+        Object b = new String("Hello!");
+
+        assertThrows(NullPointerException.class, () -> a.equals(b));
+    }
+
+    @Test
+    void givenTwoObjectsSecondNull_whenEquals_thenFalse() {
+        Object a = new String("Hello!");
+        Object b = null;
+
+        assertThat(a.equals(b)).isFalse();
+    }
+
+    @Test
+    void givenTwoPersonWithoutEqualsWithSameNames_whenEquals_thenFalse() {
+        PersonWithoutEquals joe = new PersonWithoutEquals("Joe", "Portman");
+        PersonWithoutEquals joeAgain = new PersonWithoutEquals("Joe", "Portman");
+
+        assertThat(joe.equals(joeAgain)).isFalse();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsWithSameNames_whenEquals_thenTrue() {
+        PersonWithEquals joe = new PersonWithEquals("Joe", "Portman");
+        PersonWithEquals joeAgain = new PersonWithEquals("Joe", "Portman");
+
+        assertThat(joe.equals(joeAgain)).isTrue();
+    }
+
+    @Test
+    void givenTwoPersonWittEqualsWithDifferentNames_whenEquals_thenFalse() {
+        PersonWithEquals joe = new PersonWithEquals("Joe", "Portman");
+        PersonWithEquals natalie = new PersonWithEquals("Natalie", "Portman");
+
+        assertThat(joe.equals(natalie)).isFalse();
+    }
+}

core-java-modules/core-java-lang-2/src/test/java/com/baeldung/comparing/GuavaUnitTest.java

@@ -0,0 +1,73 @@
+package com.baeldung.comparing;
+
+import com.google.common.base.Objects;
+import com.google.common.collect.ComparisonChain;
+import com.google.common.primitives.Ints;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class GuavaUnitTest {
+
+    @Nested
+    class ObjectsEqualMethod {
+        @Test
+        void givenTwoStringsWithSameValues_whenObjectsEqualMethods_thenTrue() {
+            String a = new String("Hello!");
+            String b = new String("Hello!");
+
+            assertThat(Objects.equal(a, b)).isTrue();
+        }
+
+        @Test
+        void givenTwoStringsWithDifferentValues_whenObjectsEqualMethods_thenFalse() {
+            String a = new String("Hello!");
+            String b = new String("Hello World!");
+
+            assertThat(Objects.equal(a, b)).isFalse();
+        }
+    }
+
+    @Nested
+    class ComparisonMethods {
+        @Test
+        void givenTwoIntsWithConsecutiveValues_whenIntsCompareMethods_thenNegative() {
+            int first = 1;
+            int second = 2;
+            assertThat(Ints.compare(first, second)).isNegative();
+        }
+
+        @Test
+        void givenTwoIntsWithSameValues_whenIntsCompareMethods_thenZero() {
+            int first = 1;
+            int second = 1;
+
+            assertThat(Ints.compare(first, second)).isZero();
+        }
+
+        @Test
+        void givenTwoIntsWithConsecutiveValues_whenIntsCompareMethodsReversed_thenNegative() {
+            int first = 1;
+            int second = 2;
+
+            assertThat(Ints.compare(second, first)).isPositive();
+        }
+    }
+
+    @Nested
+    class ComparisonChainClass {
+        @Test
+        void givenTwoPersonWithEquals_whenComparisonChainByLastNameThenFirstName_thenSortedJoeFirstAndNatalieSecond() {
+            PersonWithEquals natalie = new PersonWithEquals("Natalie", "Portman");
+            PersonWithEquals joe = new PersonWithEquals("Joe", "Portman");
+
+            int comparisonResult = ComparisonChain.start()
+              .compare(natalie.lastName(), joe.lastName())
+              .compare(natalie.firstName(), joe.firstName())
+              .result();
+
+            assertThat(comparisonResult).isPositive();
+        }
+    }
+}

core-java-modules/core-java-lang-2/src/test/java/com/baeldung/comparing/ObjectsEqualsStaticMethodUnitTest.java

@@ -0,0 +1,50 @@
+package com.baeldung.comparing;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Objects;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class ObjectsEqualsStaticMethodUnitTest {
+
+    @Test
+    void givenTwoPersonWithEqualsWithSameNames_whenObjectsEquals_thenTrue() {
+        PersonWithEquals joe = new PersonWithEquals("Joe", "Portman");
+        PersonWithEquals joeAgain = new PersonWithEquals("Joe", "Portman");
+
+        assertThat(Objects.equals(joe, joeAgain)).isTrue();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsWithDifferentNames_whenObjectsEquals_thenFalse() {
+        PersonWithEquals joe = new PersonWithEquals("Joe", "Portman");
+        PersonWithEquals natalie = new PersonWithEquals("Natalie", "Portman");
+
+        assertThat(Objects.equals(joe, natalie)).isFalse();
+    }
+
+    @Test
+    void givenTwoPersonWithEqualsFirstNull_whenObjectsEquals_thenFalse() {
+        PersonWithEquals nobody = null;
+        PersonWithEquals joe = new PersonWithEquals("Joe", "Portman");
+
+        assertThat(Objects.equals(nobody, joe)).isFalse();
+    }
+
+    @Test
+    void givenTwoObjectsSecondtNull_whenObjectsEquals_thenFalse() {
+        PersonWithEquals joe = new PersonWithEquals("Joe", "Portman");
+        PersonWithEquals nobody = null;
+
+        assertThat(Objects.equals(joe, nobody)).isFalse();
+    }
+
+    @Test
+    void givenTwoObjectsNull_whenObjectsEquals_thenTrue() {
+        PersonWithEquals nobody = null;
+        PersonWithEquals nobodyAgain = null;
+
+        assertThat(Objects.equals(nobody, nobodyAgain)).isTrue();
+    }
+}

core-java-modules/core-java-lang-oop-2/.gitignore

@@ -1,4 +0,0 @@
-target/
-.idea/
-bin/
-*.iml

core-java-modules/core-java-lang-oop-2/README.md

@@ -1,18 +0,0 @@
-## Core Java Lang OOP (Part 2)
-
-This module contains articles about Object-oriented programming (OOP) in Java
-
-### Relevant Articles: 
-- [Generic Constructors in Java](https://www.baeldung.com/java-generic-constructors)
-- [Cannot Reference “X” Before Supertype Constructor Has Been Called](https://www.baeldung.com/java-cannot-reference-x-before-supertype-constructor-error)
-- [Anonymous Classes in Java](https://www.baeldung.com/java-anonymous-classes)
-- [Raw Types in Java](https://www.baeldung.com/raw-types-java)
-- [Marker Interfaces in Java](https://www.baeldung.com/java-marker-interfaces)
-- [Java equals() and hashCode() Contracts](https://www.baeldung.com/java-equals-hashcode-contracts)
-- [Immutable Objects in Java](https://www.baeldung.com/java-immutable-object)
-- [Inheritance and Composition (Is-a vs Has-a relationship) in Java](https://www.baeldung.com/java-inheritance-composition)
-- [A Guide to Constructors in Java](https://www.baeldung.com/java-constructors)
-- [Static and Default Methods in Interfaces in Java](https://www.baeldung.com/java-static-default-methods)
-- [Java Copy Constructor](https://www.baeldung.com/java-copy-constructor)
-- [Abstract Classes in Java](https://www.baeldung.com/java-abstract-class)
-- [[<-- Prev]](/core-java-modules/core-java-lang-oop)[[More -->]](/core-java-modules/core-java-lang-oop-3)

core-java-modules/core-java-lang-oop-2/pom.xml

@@ -1,51 +0,0 @@
-<?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-lang-oop-2</artifactId>
-    <version>0.1.0-SNAPSHOT</version>
-    <name>core-java-lang-oop-2</name>
-    <packaging>jar</packaging>
-
-    <parent>
-        <groupId>com.baeldung</groupId>
-        <artifactId>parent-java</artifactId>
-        <version>0.0.1-SNAPSHOT</version>
-        <relativePath>../../parent-java</relativePath>
-    </parent>
-
-    <dependencies>
-        <!-- test scoped -->
-        <dependency>
-            <groupId>org.assertj</groupId>
-            <artifactId>assertj-core</artifactId>
-            <version>${assertj-core.version}</version>
-            <scope>test</scope>
-        </dependency>
-        <dependency>
-            <groupId>nl.jqno.equalsverifier</groupId>
-            <artifactId>equalsverifier</artifactId>
-            <version>${equalsverifier.version}</version>
-            <scope>test</scope>
-        </dependency>
-    </dependencies>
-
-    <build>
-        <finalName>core-java-lang-oop-2</finalName>
-        <resources>
-            <resource>
-                <directory>src/main/resources</directory>
-                <filtering>true</filtering>
-            </resource>
-        </resources>
-    </build>
-
-    <properties>
-        <!-- testing -->
-        <assertj-core.version>3.10.0</assertj-core.version>
-        <equalsverifier.version>3.0.3</equalsverifier.version>
-    </properties>
-
-</project>

core-java-modules/core-java-lang-oop-3/README.md

@@ -1,16 +0,0 @@
-## Core Java Lang OOP (Part 3)
-
-This module contains articles about Object-oriented programming (OOP) in Java
-
-### Relevant Articles: 
-- [Pass-By-Value as a Parameter Passing Mechanism in Java](https://www.baeldung.com/java-pass-by-value-or-pass-by-reference)
-- [Access Modifiers in Java](https://www.baeldung.com/java-access-modifiers)
-- [Guide to the super Java Keyword](https://www.baeldung.com/java-super)
-- [Guide to the this Java Keyword](https://www.baeldung.com/java-this)
-- [Java ‘public’ Access Modifier](https://www.baeldung.com/java-public-keyword)
-- [Composition, Aggregation, and Association in Java](https://www.baeldung.com/java-composition-aggregation-association)
-- [Nested Classes in Java](https://www.baeldung.com/java-nested-classes)
-- [A Guide to Inner Interfaces in Java](https://www.baeldung.com/java-inner-interfaces)
-- [Java Classes and Objects](https://www.baeldung.com/java-classes-objects)
-- [Java Interfaces](https://www.baeldung.com/java-interfaces)
-- [[<-- Prev]](/core-java-modules/core-java-lang-oop-2)[[More -->]](/core-java-modules/core-java-lang-oop-4)

core-java-modules/core-java-lang-oop-3/pom.xml

@@ -1,60 +0,0 @@
-<?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-lang-oop-3</artifactId>
-    <version>0.1.0-SNAPSHOT</version>
-    <name>core-java-lang-oop-3</name>
-    <packaging>jar</packaging>
-
-    <parent>
-        <groupId>com.baeldung</groupId>
-        <artifactId>parent-java</artifactId>
-        <version>0.0.1-SNAPSHOT</version>
-        <relativePath>../../parent-java</relativePath>
-    </parent>
-
-    <dependencies>
-        <!-- logging -->
-        <dependency>
-            <groupId>log4j</groupId>
-            <artifactId>log4j</artifactId>
-            <version>${log4j.version}</version>
-        </dependency>
-        <dependency> <!-- needed to bridge to slf4j for projects that use the log4j APIs directly -->
-            <groupId>org.slf4j</groupId>
-            <artifactId>log4j-over-slf4j</artifactId>
-            <version>${org.slf4j.version}</version>
-        </dependency>
-        <!-- test scoped -->
-        <dependency>
-            <groupId>org.assertj</groupId>
-            <artifactId>assertj-core</artifactId>
-            <version>${assertj-core.version}</version>
-            <scope>test</scope>
-        </dependency>
-        <dependency>
-            <groupId>com.h2database</groupId>
-            <artifactId>h2</artifactId>
-            <version>${h2.version}</version>
-            <scope>test</scope>
-        </dependency>
-    </dependencies>
-
-    <build>
-        <finalName>core-java-lang-oop-3</finalName>
-        <resources>
-            <resource>
-                <directory>src/main/resources</directory>
-                <filtering>true</filtering>
-            </resource>
-        </resources>
-    </build>
-
-    <properties>
-        <assertj-core.version>3.10.0</assertj-core.version>
-    </properties>
-
-</project>

core-java-modules/core-java-lang-oop-4/README.md

@@ -1,9 +0,0 @@
-## Core Java Lang OOP (Part 4)
-
-This module contains articles about Object-oriented programming (OOP) in Java
-
-### Relevant Articles: 
-- [Static and Dynamic Binding in Java](https://www.baeldung.com/java-static-dynamic-binding)
-- [Methods in Java](https://www.baeldung.com/java-methods)
-- [Java ‘private’ Access Modifier](https://www.baeldung.com/java-private-keyword)
-- [[<-- Prev]](/core-java-modules/core-java-lang-oop-3)

core-java-modules/core-java-lang-oop-4/pom.xml

@@ -1,60 +0,0 @@
-<?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-lang-oop-4</artifactId>
-    <version>0.1.0-SNAPSHOT</version>
-    <name>core-java-lang-oop-4</name>
-    <packaging>jar</packaging>
-
-    <parent>
-        <groupId>com.baeldung</groupId>
-        <artifactId>parent-java</artifactId>
-        <version>0.0.1-SNAPSHOT</version>
-        <relativePath>../../parent-java</relativePath>
-    </parent>
-
-    <dependencies>
-        <!-- logging -->
-        <dependency>
-            <groupId>log4j</groupId>
-            <artifactId>log4j</artifactId>
-            <version>${log4j.version}</version>
-        </dependency>
-        <dependency> <!-- needed to bridge to slf4j for projects that use the log4j APIs directly -->
-            <groupId>org.slf4j</groupId>
-            <artifactId>log4j-over-slf4j</artifactId>
-            <version>${org.slf4j.version}</version>
-        </dependency>
-        <!-- test scoped -->
-        <dependency>
-            <groupId>org.assertj</groupId>
-            <artifactId>assertj-core</artifactId>
-            <version>${assertj-core.version}</version>
-            <scope>test</scope>
-        </dependency>
-        <dependency>
-            <groupId>com.h2database</groupId>
-            <artifactId>h2</artifactId>
-            <version>${h2.version}</version>
-            <scope>test</scope>
-        </dependency>
-    </dependencies>
-
-    <build>
-        <finalName>core-java-lang-oop-4</finalName>
-        <resources>
-            <resource>
-                <directory>src/main/resources</directory>
-                <filtering>true</filtering>
-            </resource>
-        </resources>
-    </build>
-
-    <properties>
-        <assertj-core.version>3.10.0</assertj-core.version>
-    </properties>
-
-</project>

core-java-modules/core-java-lang-oop-constructors/README.md

@@ -0,0 +1,8 @@
+## Core Java Lang OOP - Constructors
+
+This module contains article about constructors in Java
+
+### Relevant Articles:
+- [A Guide to Constructors in Java](https://www.baeldung.com/java-constructors)
+- [Java Copy Constructor](https://www.baeldung.com/java-copy-constructor)
+- [Cannot Reference “X” Before Supertype Constructor Has Been Called](https://www.baeldung.com/java-cannot-reference-x-before-supertype-constructor-error)

core-java-modules/core-java-lang-oop-constructors/pom.xml

@@ -0,0 +1,28 @@
+<?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">
+    <parent>
+        <artifactId>core-java-modules</artifactId>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>core-java-lang-oop-constructors</artifactId>
+    <name>core-java-lang-oop-constructors</name>
+    <packaging>jar</packaging>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <assertj-core.version>3.10.0</assertj-core.version>
+    </properties>
+</project>

core-java-modules/core-java-lang-oop-constructors/src/main/java/com/baeldung/constructors/BankAccount.java

@@ -54,7 +54,6 @@ class BankAccountCopyConstructor extends BankAccount {
         this.balance = 0.0f;
     }
 }
-
 class BankAccountChainedConstructors extends BankAccount {
     public BankAccountChainedConstructors(String name, LocalDateTime opened, double balance) {
         this.name = name;

core-java-modules/core-java-lang-oop-constructors/src/test/java/com/baeldung/constructors/ConstructorUnitTest.java

@@ -1,20 +1,19 @@
 package com.baeldung.constructors;
 
+import org.assertj.core.api.Assertions;
 import org.junit.Test;
 
 import java.time.LocalDateTime;
 import java.time.Month;
-import java.util.logging.Logger;
 
-import static org.assertj.core.api.Assertions.*;
+import static org.assertj.core.api.Assertions.assertThat;
 
 public class ConstructorUnitTest {
-    final static Logger LOGGER = Logger.getLogger(ConstructorUnitTest.class.getName());
     
     @Test
     public void givenNoExplicitContructor_whenUsed_thenFails() {
         BankAccount account = new BankAccount();
-        assertThatThrownBy(() -> {
+        Assertions.assertThatThrownBy(() -> {
             account.toString();
         }).isInstanceOf(Exception.class);
     }
@@ -22,7 +21,7 @@ public class ConstructorUnitTest {
     @Test
     public void givenNoArgumentConstructor_whenUsed_thenSucceeds() {
         BankAccountEmptyConstructor account = new BankAccountEmptyConstructor();
-        assertThatCode(() -> {
+        Assertions.assertThatCode(() -> {
             account.toString();
         }).doesNotThrowAnyException();
     }
@@ -33,7 +32,7 @@ public class ConstructorUnitTest {
         BankAccountParameterizedConstructor account =
                 new BankAccountParameterizedConstructor("Tom", opened, 1000.0f);
 
-        assertThatCode(() -> {
+        Assertions.assertThatCode(() -> {
             account.toString();
         }).doesNotThrowAnyException();
     }

core-java-modules/core-java-lang-oop-generics/README.md

@@ -0,0 +1,8 @@
+## Core Java Lang OOP - Generics
+
+This module contains articles about generics in Java
+
+### Relevant Articles: 
+- [Generic Constructors in Java](https://www.baeldung.com/java-generic-constructors)
+- [Type Erasure in Java Explained](https://www.baeldung.com/java-type-erasure)
+- [Raw Types in Java](https://www.baeldung.com/raw-types-java)

core-java-modules/core-java-lang-oop-generics/pom.xml

@@ -0,0 +1,16 @@
+<?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">
+    <parent>
+        <artifactId>core-java-modules</artifactId>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>core-java-lang-oop-generics</artifactId>
+    <name>core-java-lang-oop-generics</name>
+    <packaging>jar</packaging>
+
+</project>