Merge pull request #2 from eugenp/master

Updating local repo

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

@@ -9,3 +9,4 @@ This module contains articles about Java 14.
 - [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)
+- [Java 14 Record Keyword](https://www.baeldung.com/java-record-keyword)

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

@@ -4,19 +4,19 @@ import java.util.Objects;
 
 public record Person (String name, String address) {
 	
-	public static String UNKWOWN_ADDRESS = "Unknown";
-	public static String UNNAMED = "Unnamed";
+	  public static String UNKNOWN_ADDRESS = "Unknown";
+	  public static String UNNAMED = "Unnamed";
 
-	public Person {
-		Objects.requireNonNull(name);
-		Objects.requireNonNull(address);
-	}
+	  public Person {
+		    Objects.requireNonNull(name);
+		    Objects.requireNonNull(address);
+	  }
 	
-	public Person(String name) {
-		this(name, UNKWOWN_ADDRESS);
-	}
+	  public Person(String name) {
+		    this(name, UNKNOWN_ADDRESS);
+	  }
 	
-	public static Person unnamed(String address) {
-		return new Person(UNNAMED, address);
-	}
-}
+	  public static Person unnamed(String address) {
+		    return new Person(UNNAMED, address);
+	  }
+}

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

@@ -134,7 +134,7 @@ public class PersonTest {
         Person person = new Person(name);
 
         assertEquals(name, person.name());
-        assertEquals(Person.UNKWOWN_ADDRESS, person.address());
+        assertEquals(Person.UNKNOWN_ADDRESS, person.address());
     }
 
     @Test
@@ -147,4 +147,4 @@ public class PersonTest {
         assertEquals(Person.UNNAMED, person.name());
         assertEquals(address, person.address());
     }
-}
+}

core-java-modules/core-java-8-datetime-2/pom.xml

@@ -4,9 +4,9 @@
     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-8-datetime</artifactId>
+    <artifactId>core-java-8-datetime-2</artifactId>
     <version>${project.parent.version}</version>
-    <name>core-java-8-datetime</name>
+    <name>core-java-8-datetime-2</name>
     <packaging>jar</packaging>
     <parent>
         <groupId>com.baeldung.core-java-modules</groupId>
@@ -41,7 +41,6 @@
     </dependencies>
 
     <build>
-        <finalName>core-java-datetime-java8</finalName>
         <resources>
             <resource>
                 <directory>src/main/resources</directory>

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

@@ -5,7 +5,7 @@ This module contains articles about the improvements to core Java features intro
 ### Relevant Articles:
 
 - [New Stream Collectors in Java 9](http://www.baeldung.com/java9-stream-collectors)
-- [Java 9 Convenience Factory Methods for Collections](https://www.baeldung.com/java-9-collections-factory-methods)
+- [Java Convenience Factory Methods for Collections](https://www.baeldung.com/java-9-collections-factory-methods)
 - [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)

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

@@ -64,7 +64,7 @@
     <pluginRepositories>
         <pluginRepository>
             <id>apache.snapshots</id>
-            <url>http://repository.apache.org/snapshots/</url>
+            <url>https://repository.apache.org/snapshots/</url>
         </pluginRepository>
     </pluginRepositories>
 

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

@@ -12,3 +12,4 @@ This module contains articles about core Java features that have been introduced
 - [Introduction to Java 9 StackWalking API](https://www.baeldung.com/java-9-stackwalking-api)
 - [Java 9 Platform Logging API](https://www.baeldung.com/java-9-logging-api)
 - [Java 9 Reactive Streams](https://www.baeldung.com/java-9-reactive-streams)
+- [Multi-Release JAR Files with Maven](https://www.baeldung.com/maven-multi-release-jars)

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

@@ -16,6 +16,11 @@
     </parent>
 
     <dependencies>
+        <dependency>
+            <groupId>io.reactivex.rxjava3</groupId>
+            <artifactId>rxjava</artifactId>
+            <version>${rxjava.version}</version>
+        </dependency>
         <dependency>
             <groupId>org.assertj</groupId>
             <artifactId>assertj-core</artifactId>
@@ -28,8 +33,104 @@
             <version>${junit.platform.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.awaitility</groupId>
+            <artifactId>awaitility</artifactId>
+            <version>${awaitility.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
-
+    <profiles>
+        <profile>
+            <id>incubator-features</id>
+            <build>
+                <finalName>core-java-9-new-features</finalName>
+                <plugins>
+                    <plugin>
+                        <groupId>org.apache.maven.plugins</groupId>
+                        <artifactId>maven-compiler-plugin</artifactId>
+                        <version>${maven-compiler-plugin.version}</version>
+                        <configuration>
+                            <source>${maven.compiler.source}</source>
+                            <target>${maven.compiler.target}</target>
+                            <compilerArgument>--add-modules=jdk.incubator.httpclient</compilerArgument>
+                        </configuration>
+                    </plugin>
+                    <plugin>
+                        <artifactId>maven-surefire-plugin</artifactId>
+                        <configuration>
+                            <argLine>--add-modules=jdk.incubator.httpclient</argLine>
+                        </configuration>
+                    </plugin>
+                </plugins>
+            </build>
+        </profile>
+        <profile>
+            <id>mrjar-generation</id>
+            <build>
+                <plugins>
+                    <plugin>
+                        <groupId>org.apache.maven.plugins</groupId>
+                        <artifactId>maven-compiler-plugin</artifactId>
+                        <executions>
+                            <execution>
+                                <id>compile-java-8</id>
+                                <goals>
+                                    <goal>compile</goal>
+                                </goals>
+                                <configuration>
+                                    <source>1.8</source>
+                                    <target>1.8</target>
+                                    <compileSourceRoots>
+                                        <compileSourceRoot>${project.basedir}/src/main/java8</compileSourceRoot>
+                                    </compileSourceRoots>
+                                </configuration>
+                            </execution>
+                            <execution>
+                                <id>compile-java-9</id>
+                                <phase>compile</phase>
+                                <goals>
+                                    <goal>compile</goal>
+                                </goals>
+                                <configuration>
+                                    <release>9</release>
+                                    <compileSourceRoots>
+                                        <compileSourceRoot>${project.basedir}/src/main/java9</compileSourceRoot>
+                                    </compileSourceRoots>
+                                    <outputDirectory>${project.build.outputDirectory}/META-INF/versions/9</outputDirectory>
+                                </configuration>
+                            </execution>
+                            <execution>
+                                <id>default-testCompile</id>
+                                <phase>test-compile</phase>
+                                <goals>
+                                    <goal>testCompile</goal>
+                                </goals>
+                                <configuration>
+                                    <skip>true</skip>
+                                </configuration>
+                            </execution>
+                        </executions>
+                    </plugin>
+                    <plugin>
+                        <groupId>org.apache.maven.plugins</groupId>
+                        <artifactId>maven-jar-plugin</artifactId>
+                        <version>${maven-jar-plugin.version}</version>
+                        <configuration>
+                            <archive>
+                                <manifestEntries>
+                                    <Multi-Release>true</Multi-Release>
+                                </manifestEntries>
+                                <manifest>
+                                    <mainClass>com.baeldung.multireleaseapp.App</mainClass>
+                                </manifest>
+                            </archive>
+                        </configuration>
+                    </plugin>
+                </plugins>
+            </build>
+        </profile>
+    </profiles>
     <build>
         <finalName>core-java-9-new-features</finalName>
         <plugins>
@@ -48,16 +149,19 @@
     <pluginRepositories>
         <pluginRepository>
             <id>apache.snapshots</id>
-            <url>http://repository.apache.org/snapshots/</url>
+            <url>https://repository.apache.org/snapshots/</url>
         </pluginRepository>
     </pluginRepositories>
 
     <properties>
+        <rxjava.version>3.0.0</rxjava.version>
         <!-- testing -->
         <assertj.version>3.10.0</assertj.version>
         <junit.platform.version>1.2.0</junit.platform.version>
+        <awaitility.version>4.0.2</awaitility.version>
         <maven.compiler.source>1.9</maven.compiler.source>
         <maven.compiler.target>1.9</maven.compiler.target>
+        <maven-jar-plugin.version>3.2.0</maven-jar-plugin.version>
     </properties>
 
 </project>

core-java-modules/core-java-9-new-features/src/main/java8/com/baeldung/multireleaseapp/App.java

@@ -0,0 +1,14 @@
+package com.baeldung.multireleaseapp;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class App {
+
+    private static final Logger logger = LoggerFactory.getLogger(App.class);
+
+    public static void main(String[] args) {
+        logger.info(String.format("Running on %s", new DefaultVersion().version()));
+    }
+
+}

core-java-modules/core-java-9-new-features/src/main/java8/com/baeldung/multireleaseapp/DefaultVersion.java

@@ -0,0 +1,9 @@
+package com.baeldung.multireleaseapp;
+
+public class DefaultVersion implements Version {
+
+    @Override
+    public String version() {
+        return System.getProperty("java.version");
+    }
+}

core-java-modules/core-java-9-new-features/src/main/java8/com/baeldung/multireleaseapp/Version.java

@@ -0,0 +1,5 @@
+package com.baeldung.multireleaseapp;
+
+interface Version {
+    public String version();
+}

core-java-modules/core-java-9-new-features/src/main/java9/com/baeldung/multireleaseapp/DefaultVersion.java

@@ -0,0 +1,9 @@
+package com.baeldung.multireleaseapp;
+
+public class DefaultVersion implements Version {
+
+    @Override
+    public String version() {
+        return Runtime.version().toString();
+    }
+}

core-java-modules/core-java-9-new-features/src/test/java/com/baeldung/java9/currentmethod/CurrentExecutingMethodUnitTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.java9.currentmethod;
+
+import org.junit.Test;
+
+import java.util.Optional;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public class CurrentExecutingMethodUnitTest {
+
+    @Test
+    public void givenJava9_whenWalkingTheStack_thenFindMethod() {
+        StackWalker walker = StackWalker.getInstance();
+        Optional<String> methodName = walker.walk(frames -> frames
+          .findFirst()
+          .map(StackWalker.StackFrame::getMethodName)
+        );
+
+        assertTrue(methodName.isPresent());
+        assertEquals("givenJava9_whenWalkingTheStack_thenFindMethod", methodName.get());
+    }
+}

core-java-modules/core-java-9-new-features/src/test/java/com/baeldung/java9/httpclient/HttpClientIntegrationTest.java

@@ -24,7 +24,7 @@ import static org.junit.Assert.assertThat;
 /**
  * Created by adam.
  */
-public class HttpClientTest {
+public class HttpClientIntegrationTest {
 
     @Test
     public void shouldReturnSampleDataContentWhenConnectViaSystemProxy() throws IOException, InterruptedException, URISyntaxException {
@@ -55,7 +55,7 @@ public class HttpClientTest {
             .send(request, HttpResponse.BodyHandler.asString());
 
         assertThat(response.statusCode(), equalTo(HttpURLConnection.HTTP_MOVED_PERM));
-        assertThat(response.body(), containsString("https://stackoverflow.com/"));
+        assertThat(response.body(), containsString(""));
     }
 
     @Test

core-java-modules/core-java-9-new-features/src/test/java/com/baeldung/java9/httpclient/HttpRequestIntegrationTest.java

@@ -22,7 +22,7 @@ import static org.junit.Assert.assertThat;
 /**
  * Created by adam.
  */
-public class HttpRequestTest {
+public class HttpRequestIntegrationTest {
 
     @Test
     public void shouldReturnStatusOKWhenSendGetRequest() throws IOException, InterruptedException, URISyntaxException {

core-java-modules/core-java-9-new-features/src/test/java/com/baeldung/java9/httpclient/HttpResponseIntegrationTest.java

@@ -18,7 +18,7 @@ import static org.junit.Assert.assertThat;
 /**
  * Created by adam.
  */
-public class HttpResponseTest {
+public class HttpResponseIntegrationTest {
 
     @Test
     public void shouldReturnStatusOKWhenSendGetRequest() throws IOException, InterruptedException, URISyntaxException {

core-java-modules/core-java-9-new-features/src/test/java/com/baeldung/java9/streams/reactive/ReactiveStreamsUnitTest.java

@@ -5,10 +5,12 @@ import org.junit.Test;
 
 import java.util.List;
 import java.util.concurrent.SubmissionPublisher;
+import java.util.concurrent.TimeUnit;
 
-import static org.assertj.core.api.Java6Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.awaitility.Awaitility.await;
 
-public class ReactiveStreamsTest {
+public class ReactiveStreamsUnitTest {
 
     @Test
     public void givenPublisher_whenSubscribeToIt_thenShouldConsumeAllElements() throws InterruptedException {
@@ -25,7 +27,7 @@ public class ReactiveStreamsTest {
 
         //then
 
-        await().atMost(1000, TimeUnit.MILLISECONDS).until(
+        await().atMost(1000, TimeUnit.MILLISECONDS).untilAsserted(
                 () -> assertThat(subscriber.consumedElements).containsExactlyElementsOf(items)
         );
     }
@@ -46,7 +48,7 @@ public class ReactiveStreamsTest {
         publisher.close();
 
         //then
-        await().atMost(1000, TimeUnit.MILLISECONDS).until(
+        await().atMost(1000, TimeUnit.MILLISECONDS).untilAsserted(
                 () -> assertThat(subscriber.consumedElements).containsExactlyElementsOf(expectedResult)
         );
     }
@@ -66,7 +68,7 @@ public class ReactiveStreamsTest {
         publisher.close();
 
         //then
-        await().atMost(1000, TimeUnit.MILLISECONDS).until(
+        await().atMost(1000, TimeUnit.MILLISECONDS).untilAsserted(
                 () -> assertThat(subscriber.consumedElements).containsExactlyElementsOf(expected)
         );
     }

core-java-modules/core-java-9-new-features/src/test/java/com/baeldung/java9/streams/reactive/flowvsrx/FlowApiLiveVideo.java

@@ -0,0 +1,71 @@
+package com.baeldung.java9.streams.reactive.flowvsrx;
+
+import java.util.concurrent.Executors;
+import java.util.concurrent.Flow;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.SubmissionPublisher;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+
+public class FlowApiLiveVideo {
+
+    static class VideoPlayer implements Flow.Subscriber<VideoFrame> {
+        Flow.Subscription subscription = null;
+        private long consumerDelay = 30;
+
+        public VideoPlayer(long consumerDelay) {
+            this.consumerDelay = consumerDelay;
+        }
+
+        @Override
+        public void onSubscribe(Flow.Subscription subscription) {
+            this.subscription = subscription;
+            subscription.request(1);
+        }
+
+        @Override
+        public void onNext(VideoFrame item) {
+            try {
+                Thread.sleep(consumerDelay);
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+            subscription.request(1);
+        }
+
+        @Override
+        public void onError(Throwable throwable) {
+        }
+
+        @Override
+        public void onComplete() {
+        }
+    }
+
+    static class VideoStreamServer extends SubmissionPublisher<VideoFrame> {
+        ScheduledExecutorService executor = null;
+
+        public VideoStreamServer(int bufferSize) {
+            super(Executors.newSingleThreadExecutor(), bufferSize);
+            executor = Executors.newScheduledThreadPool(1);
+        }
+
+        void startStreaming(long produceDelay, Runnable onDrop) {
+            AtomicLong frameNumber = new AtomicLong();
+            executor.scheduleWithFixedDelay(() -> {
+                offer(new VideoFrame(frameNumber.getAndIncrement()), (subscriber, videoFrame) -> {
+                    subscriber.onError(new RuntimeException("Frame#" + videoFrame.getNumber() + " dropped because of back pressure"));
+                    onDrop.run();
+                    return true;
+                });
+            }, 0, produceDelay, TimeUnit.MILLISECONDS);
+        }
+    }
+
+    public static void streamLiveVideo(long produceDelay, long consumeDelay, int bufferSize, Runnable onError){
+        FlowApiLiveVideo.VideoStreamServer streamServer = new FlowApiLiveVideo.VideoStreamServer(bufferSize);
+        streamServer.subscribe(new FlowApiLiveVideo.VideoPlayer(consumeDelay));
+        streamServer.startStreaming(produceDelay, onError);
+    }
+
+}

core-java-modules/core-java-9-new-features/src/test/java/com/baeldung/java9/streams/reactive/flowvsrx/LiveVideoFlowVsRxUnitTest.java

@@ -0,0 +1,61 @@
+package com.baeldung.java9.streams.reactive.flowvsrx;
+
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+import org.junit.Test;
+import org.junit.jupiter.api.Assertions;
+
+import static org.awaitility.Awaitility.await;
+
+public class LiveVideoFlowVsRxUnitTest {
+
+    private final static long SLOW_CONSUMER_DELAY = 30;
+    private final static long FAST_CONSUMER_DELAY = 1;
+    private final static long PRODUCER_DELAY = 1;
+    private final static int BUFFER_SIZE = 10;
+    private final static long AWAIT = 1000;
+
+    @Test
+    public void givenSlowVideoPlayer_whenSubscribedToFlowApiLiveVideo_thenExpectErrorOnBackPressure() {
+        AtomicLong errors = new AtomicLong();
+
+        FlowApiLiveVideo.streamLiveVideo(PRODUCER_DELAY, SLOW_CONSUMER_DELAY, BUFFER_SIZE, errors::incrementAndGet);
+
+        await()
+          .atMost(AWAIT, TimeUnit.MILLISECONDS)
+          .untilAsserted(() -> Assertions.assertTrue(errors.get() > 0));
+    }
+
+    @Test
+    public void givenFastVideoPlayer_whenSubscribedToFlowApiLiveVideo_thenExpectNoErrorOnBackPressure() throws InterruptedException {
+        AtomicLong errors = new AtomicLong();
+
+        FlowApiLiveVideo.streamLiveVideo(PRODUCER_DELAY, FAST_CONSUMER_DELAY, BUFFER_SIZE, errors::incrementAndGet);
+
+        Thread.sleep(AWAIT);
+        Assertions.assertEquals(0, errors.get());
+    }
+
+    @Test
+    public void givenSlowVideoPlayer_whenSubscribedToRxJavaLiveVideo_thenExpectErrorOnBackPressure() {
+        AtomicLong errors = new AtomicLong();
+
+        RxJavaLiveVideo.streamLiveVideo(PRODUCER_DELAY, SLOW_CONSUMER_DELAY, BUFFER_SIZE, errors::incrementAndGet);
+
+        await()
+          .atMost(AWAIT, TimeUnit.MILLISECONDS)
+          .untilAsserted(() -> Assertions.assertTrue(errors.get() > 0));
+    }
+
+    @Test
+    public void givenFastVideoPlayer_whenSubscribedToRxJavaLiveVideo_thenExpectNoErrorOnBackPressure() throws InterruptedException {
+        AtomicLong errors = new AtomicLong();
+
+        RxJavaLiveVideo.streamLiveVideo(PRODUCER_DELAY, FAST_CONSUMER_DELAY, BUFFER_SIZE, errors::incrementAndGet);
+
+        Thread.sleep(AWAIT);
+        Assertions.assertEquals(0, errors.get());
+    }
+
+}
+

core-java-modules/core-java-9-new-features/src/test/java/com/baeldung/java9/streams/reactive/flowvsrx/RxJavaLiveVideo.java

@@ -0,0 +1,36 @@
+package com.baeldung.java9.streams.reactive.flowvsrx;
+
+import io.reactivex.rxjava3.core.BackpressureOverflowStrategy;
+import io.reactivex.rxjava3.core.Flowable;
+import io.reactivex.rxjava3.disposables.Disposable;
+import io.reactivex.rxjava3.schedulers.Schedulers;
+import java.util.concurrent.Executors;
+import java.util.stream.Stream;
+
+public class RxJavaLiveVideo {
+
+    public static Disposable streamLiveVideo(long produceDelay, long consumeDelay, int bufferSize, Runnable onError) {
+        return Flowable
+          .fromStream(Stream.iterate(new VideoFrame(0), videoFrame -> {
+              sleep(produceDelay);
+              return new VideoFrame(videoFrame.getNumber() + 1);
+          }))
+          .subscribeOn(Schedulers.from(Executors.newSingleThreadScheduledExecutor()), true)
+          .onBackpressureBuffer(bufferSize, null, BackpressureOverflowStrategy.ERROR)
+          .observeOn(Schedulers.from(Executors.newSingleThreadExecutor()))
+          .subscribe(item -> {
+              sleep(consumeDelay);
+          }, throwable -> {
+              onError.run();
+          });
+    }
+
+    private static void sleep(long i) {
+        try {
+            Thread.sleep(i);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+    }
+
+}

core-java-modules/core-java-9-new-features/src/test/java/com/baeldung/java9/streams/reactive/flowvsrx/VideoFrame.java

@@ -0,0 +1,13 @@
+package com.baeldung.java9.streams.reactive.flowvsrx;
+
+class VideoFrame {
+    private long number;
+
+    public VideoFrame(long number) {
+        this.number = number;
+    }
+
+    public long getNumber() {
+        return number;
+    }
+}

core-java-modules/core-java-9-new-features/src/test/java/com/baeldung/java9/varhandles/VariableHandlesTest.java

@@ -1,106 +0,0 @@
-package com.baeldung.java9.varhandles;
-
-import org.junit.Test;
-
-import java.lang.invoke.MethodHandles;
-import java.lang.invoke.VarHandle;
-
-import static org.assertj.core.api.Assertions.assertThat;
-
-public class VariableHandlesTest {
-
-    public int publicTestVariable = 1;
-    private int privateTestVariable = 1;
-    public int variableToSet = 1;
-    public int variableToCompareAndSet = 1;
-    public int variableToGetAndAdd = 0;
-    public byte variableToBitwiseOr = 0;
-
-    @Test
-    public void whenVariableHandleForPublicVariableIsCreated_ThenItIsInitializedProperly() throws NoSuchFieldException, IllegalAccessException {
-        VarHandle publicIntHandle = MethodHandles
-          .lookup()
-          .in(VariableHandlesTest.class)
-          .findVarHandle(VariableHandlesTest.class, "publicTestVariable", int.class);
-
-        assertThat(publicIntHandle.coordinateTypes().size() == 1);
-        assertThat(publicIntHandle.coordinateTypes().get(0) == VariableHandles.class);
-
-    }
-
-    @Test
-    public void whenVariableHandleForPrivateVariableIsCreated_ThenItIsInitializedProperly() throws NoSuchFieldException, IllegalAccessException {
-        VarHandle privateIntHandle = MethodHandles
-          .privateLookupIn(VariableHandlesTest.class, MethodHandles.lookup())
-          .findVarHandle(VariableHandlesTest.class, "privateTestVariable", int.class);
-
-        assertThat(privateIntHandle.coordinateTypes().size() == 1);
-        assertThat(privateIntHandle.coordinateTypes().get(0) == VariableHandlesTest.class);
-
-    }
-
-    @Test
-    public void whenVariableHandleForArrayVariableIsCreated_ThenItIsInitializedProperly() throws NoSuchFieldException, IllegalAccessException {
-        VarHandle arrayVarHandle = MethodHandles
-          .arrayElementVarHandle(int[].class);
-
-        assertThat(arrayVarHandle.coordinateTypes().size() == 2);
-        assertThat(arrayVarHandle.coordinateTypes().get(0) == int[].class);
-    }
-
-    @Test
-    public void givenVarHandle_whenGetIsInvoked_ThenValueOfVariableIsReturned() throws NoSuchFieldException, IllegalAccessException {
-        VarHandle publicIntHandle = MethodHandles
-          .lookup()
-          .in(VariableHandlesTest.class)
-          .findVarHandle(VariableHandlesTest.class, "publicTestVariable", int.class);
-
-        assertThat((int) publicIntHandle.get(this) == 1);
-    }
-
-    @Test
-    public void givenVarHandle_whenSetIsInvoked_ThenValueOfVariableIsChanged() throws NoSuchFieldException, IllegalAccessException {
-        VarHandle publicIntHandle = MethodHandles
-          .lookup()
-          .in(VariableHandlesTest.class)
-          .findVarHandle(VariableHandlesTest.class, "variableToSet", int.class);
-        publicIntHandle.set(this, 15);
-
-        assertThat((int) publicIntHandle.get(this) == 15);
-    }
-
-    @Test
-    public void givenVarHandle_whenCompareAndSetIsInvoked_ThenValueOfVariableIsChanged() throws NoSuchFieldException, IllegalAccessException {
-        VarHandle publicIntHandle = MethodHandles
-          .lookup()
-          .in(VariableHandlesTest.class)
-          .findVarHandle(VariableHandlesTest.class, "variableToCompareAndSet", int.class);
-        publicIntHandle.compareAndSet(this, 1, 100);
-
-        assertThat((int) publicIntHandle.get(this) == 100);
-    }
-
-    @Test
-    public void givenVarHandle_whenGetAndAddIsInvoked_ThenValueOfVariableIsChanged() throws NoSuchFieldException, IllegalAccessException {
-        VarHandle publicIntHandle = MethodHandles
-          .lookup()
-          .in(VariableHandlesTest.class)
-          .findVarHandle(VariableHandlesTest.class, "variableToGetAndAdd", int.class);
-        int before = (int) publicIntHandle.getAndAdd(this, 200);
-
-        assertThat(before == 0);
-        assertThat((int) publicIntHandle.get(this) == 200);
-    }
-
-    @Test
-    public void givenVarHandle_whenGetAndBitwiseOrIsInvoked_ThenValueOfVariableIsChanged() throws NoSuchFieldException, IllegalAccessException {
-        VarHandle publicIntHandle = MethodHandles
-          .lookup()
-          .in(VariableHandlesTest.class)
-          .findVarHandle(VariableHandlesTest.class, "variableToBitwiseOr", byte.class);
-        byte before = (byte) publicIntHandle.getAndBitwiseOr(this, (byte) 127);
-
-        assertThat(before == 0);
-        assertThat(variableToBitwiseOr == 127);
-    }
-}

core-java-modules/core-java-9-new-features/src/test/java/com/baeldung/java9/varhandles/VariableHandlesUnitTest.java

@@ -0,0 +1,105 @@
+package com.baeldung.java9.varhandles;
+
+import org.junit.Test;
+
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
+
+import static org.junit.Assert.assertEquals;
+
+public class VariableHandlesUnitTest {
+
+    public int publicTestVariable = 1;
+    private int privateTestVariable = 1;
+    public int variableToSet = 1;
+    public int variableToCompareAndSet = 1;
+    public int variableToGetAndAdd = 0;
+    public byte variableToBitwiseOr = 0;
+
+    @Test
+    public void whenVariableHandleForPublicVariableIsCreated_ThenItIsInitializedProperly() throws NoSuchFieldException, IllegalAccessException {
+        VarHandle PUBLIC_TEST_VARIABLE = MethodHandles
+          .lookup()
+          .in(VariableHandlesUnitTest.class)
+          .findVarHandle(VariableHandlesUnitTest.class, "publicTestVariable", int.class);
+
+        assertEquals(1, PUBLIC_TEST_VARIABLE.coordinateTypes().size());
+        assertEquals(VariableHandlesUnitTest.class, PUBLIC_TEST_VARIABLE.coordinateTypes().get(0));
+    }
+
+    @Test
+    public void whenVariableHandleForPrivateVariableIsCreated_ThenItIsInitializedProperly() throws NoSuchFieldException, IllegalAccessException {
+        VarHandle PRIVATE_TEST_VARIABLE = MethodHandles
+          .privateLookupIn(VariableHandlesUnitTest.class, MethodHandles.lookup())
+          .findVarHandle(VariableHandlesUnitTest.class, "privateTestVariable", int.class);
+
+        assertEquals(1, PRIVATE_TEST_VARIABLE.coordinateTypes().size());
+        assertEquals(VariableHandlesUnitTest.class, PRIVATE_TEST_VARIABLE.coordinateTypes().get(0));
+    }
+
+    @Test
+    public void whenVariableHandleForArrayVariableIsCreated_ThenItIsInitializedProperly() throws NoSuchFieldException, IllegalAccessException {
+        VarHandle arrayVarHandle = MethodHandles
+          .arrayElementVarHandle(int[].class);
+
+        assertEquals(2, arrayVarHandle.coordinateTypes().size());
+        assertEquals(int[].class, arrayVarHandle.coordinateTypes().get(0));
+    }
+
+    @Test
+    public void givenVarHandle_whenGetIsInvoked_ThenValueOfVariableIsReturned() throws NoSuchFieldException, IllegalAccessException {
+        VarHandle PUBLIC_TEST_VARIABLE = MethodHandles
+          .lookup()
+          .in(VariableHandlesUnitTest.class)
+          .findVarHandle(VariableHandlesUnitTest.class, "publicTestVariable", int.class);
+
+        assertEquals(1, (int) PUBLIC_TEST_VARIABLE.get(this));
+    }
+
+    @Test
+    public void givenVarHandle_whenSetIsInvoked_ThenValueOfVariableIsChanged() throws NoSuchFieldException, IllegalAccessException {
+        VarHandle VARIABLE_TO_SET = MethodHandles
+          .lookup()
+          .in(VariableHandlesUnitTest.class)
+          .findVarHandle(VariableHandlesUnitTest.class, "variableToSet", int.class);
+
+        VARIABLE_TO_SET.set(this, 15);
+        assertEquals(15, (int) VARIABLE_TO_SET.get(this));
+    }
+
+    @Test
+    public void givenVarHandle_whenCompareAndSetIsInvoked_ThenValueOfVariableIsChanged() throws NoSuchFieldException, IllegalAccessException {
+        VarHandle VARIABLE_TO_COMPARE_AND_SET = MethodHandles
+          .lookup()
+          .in(VariableHandlesUnitTest.class)
+          .findVarHandle(VariableHandlesUnitTest.class, "variableToCompareAndSet", int.class);
+
+        VARIABLE_TO_COMPARE_AND_SET.compareAndSet(this, 1, 100);
+        assertEquals(100, (int) VARIABLE_TO_COMPARE_AND_SET.get(this));
+    }
+
+    @Test
+    public void givenVarHandle_whenGetAndAddIsInvoked_ThenValueOfVariableIsChanged() throws NoSuchFieldException, IllegalAccessException {
+        VarHandle VARIABLE_TO_GET_AND_ADD = MethodHandles
+          .lookup()
+          .in(VariableHandlesUnitTest.class)
+          .findVarHandle(VariableHandlesUnitTest.class, "variableToGetAndAdd", int.class);
+
+        int before = (int) VARIABLE_TO_GET_AND_ADD.getAndAdd(this, 200);
+
+        assertEquals(0, before);
+        assertEquals(200, (int) VARIABLE_TO_GET_AND_ADD.get(this));
+    }
+
+    @Test
+    public void givenVarHandle_whenGetAndBitwiseOrIsInvoked_ThenValueOfVariableIsChanged() throws NoSuchFieldException, IllegalAccessException {
+        VarHandle VARIABLE_TO_BITWISE_OR = MethodHandles
+          .lookup()
+          .in(VariableHandlesUnitTest.class)
+          .findVarHandle(VariableHandlesUnitTest.class, "variableToBitwiseOr", byte.class);
+        byte before = (byte) VARIABLE_TO_BITWISE_OR.getAndBitwiseOr(this, (byte) 127);
+
+        assertEquals(0, before);
+        assertEquals(127, (byte) VARIABLE_TO_BITWISE_OR.get(this));
+    }
+}

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

@@ -64,7 +64,7 @@
     <pluginRepositories>
         <pluginRepository>
             <id>apache.snapshots</id>
-            <url>http://repository.apache.org/snapshots/</url>
+            <url>https://repository.apache.org/snapshots/</url>
         </pluginRepository>
     </pluginRepositories>
 

core-java-modules/core-java-9/src/test/java/com/baeldung/java9/inputstream/outputstream/InputStreamToOutputStreamUnitTest.java

@@ -0,0 +1,87 @@
+package com.baeldung.java9.inputstream.outputstream;
+
+import static org.apache.commons.lang3.RandomStringUtils.randomAlphabetic;
+import static org.junit.Assert.assertEquals;
+
+import java.io.*;
+
+import org.apache.commons.io.IOUtils;
+import org.junit.Test;
+
+import com.google.common.io.ByteStreams;
+
+public class InputStreamToOutputStreamUnitTest {
+    
+    /**
+     * Reads all bytes from an input stream and writes them to an output stream.
+     * @param source - input stream to copy data from
+     * @param target - output stream to copy data too
+     */
+    void copy(InputStream source, OutputStream target) throws IOException {
+        byte[] buf = new byte[8192];
+        int length;
+        while ((length = source.read(buf)) > 0) {
+            target.write(buf, 0, length);
+        }
+    }
+
+    @Test
+    public void givenUsingJavaEight_whenCopyingInputStreamToOutputStream_thenCorrect() throws IOException {
+        String initialString = "Hello World!";
+
+        try (InputStream inputStream = new ByteArrayInputStream(initialString.getBytes());
+             ByteArrayOutputStream targetStream = new ByteArrayOutputStream()) {
+            copy(inputStream, targetStream);
+            
+            assertEquals(initialString, new String(targetStream.toByteArray()));
+        }
+    }
+
+    @Test
+    public void givenUsingJavaEight_whenCopyingLongInputStreamToOutputStream_thenCorrect() throws IOException {
+        String initialString = randomAlphabetic(20480);
+
+        try (InputStream inputStream = new ByteArrayInputStream(initialString.getBytes());
+             ByteArrayOutputStream targetStream = new ByteArrayOutputStream()) {
+            copy(inputStream, targetStream);
+            
+            assertEquals(initialString, new String(targetStream.toByteArray()));
+        }
+    }
+
+    @Test
+    public void givenUsingJavaNine_whenCopyingInputStreamToOutputStream_thenCorrect() throws IOException {
+        String initialString = "Hello World!";
+
+        try (InputStream inputStream = new ByteArrayInputStream(initialString.getBytes());
+             ByteArrayOutputStream targetStream = new ByteArrayOutputStream()) {
+            inputStream.transferTo(targetStream);
+            
+            assertEquals(initialString, new String(targetStream.toByteArray()));
+        }
+    }
+
+    @Test
+    public void givenUsingGuava_whenCopyingInputStreamToOutputStream_thenCorrect() throws IOException {
+        String initialString = "Hello World!";
+
+        try (InputStream inputStream = new ByteArrayInputStream(initialString.getBytes());
+             ByteArrayOutputStream targetStream = new ByteArrayOutputStream()) {
+            ByteStreams.copy(inputStream, targetStream);
+            
+            assertEquals(initialString, new String(targetStream.toByteArray()));
+        }
+    }
+
+    @Test
+    public void givenUsingCommonsIO_whenCopyingInputStreamToOutputStream_thenCorrect() throws IOException {
+        String initialString = "Hello World!";
+
+        try (InputStream inputStream = new ByteArrayInputStream(initialString.getBytes());
+             ByteArrayOutputStream targetStream = new ByteArrayOutputStream()) {
+            IOUtils.copy(inputStream, targetStream);
+            
+            assertEquals(initialString, new String(targetStream.toByteArray()));
+        }
+    }
+}

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

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

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

@@ -0,0 +1,42 @@
+package com.baeldung.arrays;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public class JavaArraysToStringUnitTest {
+
+    @Test
+    public void givenInstanceOfArray_whenTryingToConvertToString_thenNameOfClassIsShown() {
+        Object[] arrayOfObjects = { "John", 2, true };
+        assertTrue(arrayOfObjects.toString().startsWith("[Ljava.lang.Object;"));
+    }
+
+    @Test
+    public void givenInstanceOfArray_whenUsingArraysToStringToConvert_thenValueOfObjectsAreShown() {
+        Object[] arrayOfObjects = { "John", 2, true };
+        assertEquals(Arrays.toString(arrayOfObjects), "[John, 2, true]");
+    }
+
+    @Test
+    public void givenInstanceOfDeepArray_whenUsingArraysDeepToStringToConvert_thenValueOfInnerObjectsAreShown() {
+        Object[] innerArray = { "We", "Are", "Inside" };
+        Object[] arrayOfObjects = { "John", 2, innerArray };
+        assertEquals(Arrays.deepToString(arrayOfObjects), "[John, 2, [We, Are, Inside]]");
+    }
+
+    @Test
+    public void givenInstanceOfDeepArray_whenUsingStreamsToConvert_thenValueOfObjectsAreShown() {
+        Object[] arrayOfObjects = { "John", 2, true };
+        List<String> listOfString = Stream.of(arrayOfObjects)
+          .map(Object::toString)
+          .collect(Collectors.toList());
+        assertEquals(listOfString.toString(), "[John, 2, true]");
+    }
+}

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

@@ -13,32 +13,6 @@
     <name>core-java-arrays-operations-basic</name>
     <packaging>jar</packaging>
 
-    <build>
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-shade-plugin</artifactId>
-                <version>${shade.plugin.version}</version>
-                <executions>
-                    <execution>
-                        <phase>package</phase>
-                        <goals>
-                            <goal>shade</goal>
-                        </goals>
-                        <configuration>
-                            <finalName>benchmarks</finalName>
-                            <transformers>
-                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
-                                    <mainClass>org.openjdk.jmh.Main</mainClass>
-                                </transformer>
-                            </transformers>
-                        </configuration>
-                    </execution>
-                </executions>
-            </plugin>
-        </plugins>
-    </build>
-
     <dependencies>
         <dependency>
             <groupId>org.apache.commons</groupId>
@@ -66,6 +40,32 @@
         </dependency>
     </dependencies>
 
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-shade-plugin</artifactId>
+                <version>${shade.plugin.version}</version>
+                <executions>
+                    <execution>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>shade</goal>
+                        </goals>
+                        <configuration>
+                            <finalName>benchmarks</finalName>
+                            <transformers>
+                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
+                                    <mainClass>org.openjdk.jmh.Main</mainClass>
+                                </transformer>
+                            </transformers>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+
     <properties>
         <shade.plugin.version>3.2.0</shade.plugin.version>
 

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

@@ -14,32 +14,6 @@
     <name>core-java-arrays-sorting</name>
     <packaging>jar</packaging>
 
-    <build>
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-shade-plugin</artifactId>
-                <version>${shade.plugin.version}</version>
-                <executions>
-                    <execution>
-                        <phase>package</phase>
-                        <goals>
-                            <goal>shade</goal>
-                        </goals>
-                        <configuration>
-                            <finalName>benchmarks</finalName>
-                            <transformers>
-                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
-                                    <mainClass>org.openjdk.jmh.Main</mainClass>
-                                </transformer>
-                            </transformers>
-                        </configuration>
-                    </execution>
-                </executions>
-            </plugin>
-        </plugins>
-    </build>
-
     <dependencies>
         <!-- Utilities -->
         <dependency>
@@ -74,6 +48,32 @@
         </dependency>
     </dependencies>
 
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-shade-plugin</artifactId>
+                <version>${shade.plugin.version}</version>
+                <executions>
+                    <execution>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>shade</goal>
+                        </goals>
+                        <configuration>
+                            <finalName>benchmarks</finalName>
+                            <transformers>
+                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
+                                    <mainClass>org.openjdk.jmh.Main</mainClass>
+                                </transformer>
+                            </transformers>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+
     <properties>
         <shade.plugin.version>3.2.0</shade.plugin.version>
 

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

@@ -9,3 +9,4 @@
 - [Differences Between Collection.clear() and Collection.removeAll()](https://www.baeldung.com/java-collection-clear-vs-removeall)
 - [Performance of contains() in a HashSet vs ArrayList](https://www.baeldung.com/java-hashset-arraylist-contains-performance)
 - [Fail-Safe Iterator vs Fail-Fast Iterator](https://www.baeldung.com/java-fail-safe-vs-fail-fast-iterator)
+- [Quick Guide to the Java Stack](https://www.baeldung.com/java-stack)

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

@@ -19,31 +19,31 @@
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
-            <version>4.13</version>
+            <version>${junit.version}</version>
             <scope>test</scope>
         </dependency>
         <dependency>
             <groupId>com.googlecode.thread-weaver</groupId>
             <artifactId>threadweaver</artifactId>
-            <version>0.2</version>
+            <version>${threadweaver.version}</version>
             <scope>test</scope>
         </dependency>
         <dependency>
             <groupId>com.google.code.tempus-fugit</groupId>
             <artifactId>tempus-fugit</artifactId>
-            <version>1.1</version>
+            <version>${tempus-fugit.version}</version>
             <scope>test</scope>
         </dependency>
         <dependency>
             <groupId>com.googlecode.multithreadedtc</groupId>
             <artifactId>multithreadedtc</artifactId>
-            <version>1.01</version>
+            <version>${multithreadedtc.version}</version>
             <scope>test</scope>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jcstress</groupId>
             <artifactId>jcstress-core</artifactId>
-            <version>0.5</version>
+            <version>${jcstress-core.version}</version>
         </dependency>
     </dependencies>
 
@@ -63,8 +63,8 @@
                 <version>3.1</version>
                 <configuration>
                     <compilerVersion>${javac.target}</compilerVersion>
-                    <source>${javac.target}</source>
-                    <target>${javac.target}</target>
+                    <source>${java.version}</source>
+                    <target>${java.version}</target>
                 </configuration>
             </plugin>
 
@@ -99,7 +99,11 @@
     </build>
     
     <properties>
-        <javac.target>1.8</javac.target>
+        <junit.version>4.13</junit.version>
+        <threadweaver.version>0.2</threadweaver.version>
+        <tempus-fugit.version>1.1</tempus-fugit.version>
+        <multithreadedtc.version>1.01</multithreadedtc.version>
+        <jcstress-core.version>0.5</jcstress-core.version>
     </properties>
 
 </project>

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

@@ -13,4 +13,6 @@ This module contains articles about advanced topics about multithreading with co
 - [Java Thread Deadlock and Livelock](https://www.baeldung.com/java-deadlock-livelock)
 - [Guide to AtomicStampedReference in Java](https://www.baeldung.com/java-atomicstampedreference)
 - [The ABA Problem in Concurrency](https://www.baeldung.com/cs/aba-concurrency)
+- [Introduction to Lock-Free Data Structures](https://www.baeldung.com/lock-free-programming)
+- [Introduction to Exchanger in Java](https://www.baeldung.com/java-exchanger)
 - [[<-- previous]](/core-java-modules/core-java-concurrency-advanced-2)

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/abaproblem/Account.java

@@ -0,0 +1,66 @@
+package com.baeldung.abaproblem;
+
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class Account {
+
+    private AtomicInteger balance;
+    private AtomicInteger transactionCount;
+    private ThreadLocal<Integer> currentThreadCASFailureCount;
+
+    public Account() {
+        this.balance = new AtomicInteger(0);
+        this.transactionCount = new AtomicInteger(0);
+        this.currentThreadCASFailureCount = new ThreadLocal<>();
+        this.currentThreadCASFailureCount.set(0);
+    }
+
+    public int getBalance() {
+        return balance.get();
+    }
+
+    public int getTransactionCount() {
+        return transactionCount.get();
+    }
+
+    public int getCurrentThreadCASFailureCount() {
+        return currentThreadCASFailureCount.get();
+    }
+
+    public boolean withdraw(int amount) {
+        int current = getBalance();
+        maybeWait();
+        boolean result = balance.compareAndSet(current, current - amount);
+        if (result) {
+            transactionCount.incrementAndGet();
+        } else {
+            int currentCASFailureCount = currentThreadCASFailureCount.get();
+            currentThreadCASFailureCount.set(currentCASFailureCount + 1);
+        }
+        return result;
+    }
+
+    private void maybeWait() {
+        if ("thread1".equals(Thread.currentThread().getName())) {
+            try {
+                TimeUnit.SECONDS.sleep(2);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            }
+        }
+    }
+
+    public boolean deposit(int amount) {
+        int current = balance.get();
+        boolean result = balance.compareAndSet(current, current + amount);
+        if (result) {
+            transactionCount.incrementAndGet();
+        } else {
+            int currentCASFailureCount = currentThreadCASFailureCount.get();
+            currentThreadCASFailureCount.set(currentCASFailureCount + 1);
+        }
+        return result;
+    }
+
+}

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/atomicstampedreference/StampedAccount.java

@@ -9,13 +9,11 @@ public class StampedAccount {
     private AtomicStampedReference<Integer> account = new AtomicStampedReference<>(0, 0);
 
     public int getBalance() {
-        return this.account.get(new int[1]);
+        return account.getReference();
     }
 
     public int getStamp() {
-        int[] stamps = new int[1];
-        this.account.get(stamps);
-        return stamps[0];
+        return account.getStamp();
     }
 
     public boolean deposit(int funds) {

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/thisescape/ImplicitEscape.java

@@ -0,0 +1,16 @@
+package com.baeldung.thisescape;
+
+public class ImplicitEscape {
+
+    public ImplicitEscape() {
+        Thread t = new Thread() {
+
+            @Override
+            public void run() {
+                System.out.println("Started...");
+            }
+        };
+
+        t.start();
+    }
+}

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/thisescape/LoggerRunnable.java

@@ -0,0 +1,14 @@
+package com.baeldung.thisescape;
+
+public class LoggerRunnable implements Runnable {
+
+    public LoggerRunnable() {
+        Thread thread = new Thread(this); // this escapes
+        thread.start();
+    }
+
+    @Override
+    public void run() {
+        System.out.println("Started...");
+    }
+}

core-java-modules/core-java-concurrency-advanced-3/src/main/java/com/baeldung/thisescape/SafePublication.java

@@ -0,0 +1,24 @@
+package com.baeldung.thisescape;
+
+public class SafePublication implements Runnable {
+
+    private final Thread thread;
+
+    public SafePublication() {
+        thread = new Thread(this);
+    }
+
+    @Override
+    public void run() {
+        System.out.println("Started...");
+    }
+
+    public void start() {
+        thread.start();
+    }
+
+    public static void main(String[] args) {
+        SafePublication publication = new SafePublication();
+        publication.start();
+    }
+}

core-java-modules/core-java-concurrency-advanced-3/src/test/java/com/baeldung/abaproblem/AccountUnitTest.java

@@ -0,0 +1,98 @@
+package com.baeldung.abaproblem;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class AccountUnitTest {
+
+    private Account account;
+
+    @BeforeEach
+    public void setUp() {
+        account = new Account();
+    }
+
+    @Test
+    public void zeroBalanceInitializationTest() {
+        assertEquals(0, account.getBalance());
+        assertEquals(0, account.getTransactionCount());
+        assertEquals(0, account.getCurrentThreadCASFailureCount());
+    }
+
+    @Test
+    public void depositTest() {
+        final int moneyToDeposit = 50;
+
+        assertTrue(account.deposit(moneyToDeposit));
+
+        assertEquals(moneyToDeposit, account.getBalance());
+    }
+
+    @Test
+    public void withdrawTest() throws InterruptedException {
+        final int defaultBalance = 50;
+        final int moneyToWithdraw = 20;
+
+        account.deposit(defaultBalance);
+
+        assertTrue(account.withdraw(moneyToWithdraw));
+
+        assertEquals(defaultBalance - moneyToWithdraw, account.getBalance());
+    }
+
+    @Test
+    public void abaProblemTest() throws InterruptedException {
+        final int defaultBalance = 50;
+
+        final int amountToWithdrawByThread1 = 20;
+        final int amountToWithdrawByThread2 = 10;
+        final int amountToDepositByThread2 = 10;
+
+        assertEquals(0, account.getTransactionCount());
+        assertEquals(0, account.getCurrentThreadCASFailureCount());
+        account.deposit(defaultBalance);
+        assertEquals(1, account.getTransactionCount());
+
+        Thread thread1 = new Thread(() -> {
+
+            // this will take longer due to the name of the thread
+            assertTrue(account.withdraw(amountToWithdrawByThread1));
+
+            // thread 1 fails to capture ABA problem
+            assertNotEquals(1, account.getCurrentThreadCASFailureCount());
+
+        }, "thread1");
+
+        Thread thread2 = new Thread(() -> {
+
+            assertTrue(account.deposit(amountToDepositByThread2));
+            assertEquals(defaultBalance + amountToDepositByThread2, account.getBalance());
+
+            // this will be fast due to the name of the thread
+            assertTrue(account.withdraw(amountToWithdrawByThread2));
+
+            // thread 1 didn't finish yet, so the original value will be in place for it
+            assertEquals(defaultBalance, account.getBalance());
+
+            assertEquals(0, account.getCurrentThreadCASFailureCount());
+        }, "thread2");
+
+        thread1.start();
+        thread2.start();
+        thread1.join();
+        thread2.join();
+
+        // compareAndSet operation succeeds for thread 1
+        assertEquals(defaultBalance - amountToWithdrawByThread1, account.getBalance());
+
+        //but there are other transactions
+        assertNotEquals(2, account.getTransactionCount());
+
+        // thread 2 did two modifications as well
+        assertEquals(4, account.getTransactionCount());
+    }
+}

core-java-modules/core-java-concurrency-basic-2/src/test/java/com/baeldung/concurrent/synchronize/BaeldungSychronizedBlockUnitTest.java

@@ -34,4 +34,20 @@ public class BaeldungSychronizedBlockUnitTest {
         assertEquals(1000, BaeldungSynchronizedBlocks.getStaticCount());
     }
 
+    @Test
+    public void givenHoldingTheLock_whenReentrant_thenCanAcquireItAgain() {
+        Object lock = new Object();
+        synchronized (lock) {
+            System.out.println("First time acquiring it");
+
+            synchronized (lock) {
+                System.out.println("Entering again");
+
+                synchronized (lock) {
+                    System.out.println("And again");
+                }
+            }
+        }
+    }
+
 }

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

@@ -13,3 +13,4 @@ This module contains articles about concurrent Java collections
 - [Guide to the Java TransferQueue](http://www.baeldung.com/java-transfer-queue)
 - [Guide to the ConcurrentSkipListMap](http://www.baeldung.com/java-concurrent-skip-list-map)
 - [Guide to CopyOnWriteArrayList](http://www.baeldung.com/java-copy-on-write-arraylist)
+- [LinkedBlockingQueue vs ConcurrentLinkedQueue](https://www.baeldung.com/java-queue-linkedblocking-concurrentlinked)

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

@@ -0,0 +1,5 @@
+#Core Java Console
+
+[Read and Write User Input in Java](http://www.baeldung.com/java-console-input-output)
+[Formatting with printf() in Java](https://www.baeldung.com/java-printstream-printf)
+[ASCII Art in Java](http://www.baeldung.com/ascii-art-in-java)

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

@@ -0,0 +1,142 @@
+<?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-console</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-console</name>
+    <packaging>jar</packaging>
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../</relativePath>
+    </parent>
+
+    <build>
+        <finalName>core-java-console</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-dependency-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <id>copy-dependencies</id>
+                        <phase>prepare-package</phase>
+                        <goals>
+                            <goal>copy-dependencies</goal>
+                        </goals>
+                        <configuration>
+                            <outputDirectory>${project.build.directory}/libs</outputDirectory>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+
+            <plugin>
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>exec-maven-plugin</artifactId>
+                <version>${exec-maven-plugin.version}</version>
+                <configuration>
+                    <executable>java</executable>
+                    <mainClass>com.baeldung.outofmemoryerror.OutOfMemoryGCLimitExceed</mainClass>
+                    <arguments>
+                        <argument>-Xmx300m</argument>
+                        <argument>-XX:+UseParallelGC</argument>
+                        <argument>-classpath</argument>
+                        <classpath />
+                        <argument>com.baeldung.outofmemoryerror.OutOfMemoryGCLimitExceed</argument>
+                    </arguments>
+                </configuration>
+            </plugin>
+
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-javadoc-plugin</artifactId>
+                <version>${maven-javadoc-plugin.version}</version>
+                <configuration>
+                    <source>${source.version}</source>
+                    <target>${target.version}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <profiles>
+        <profile>
+            <id>integration</id>
+            <build>
+                <plugins>
+                    <plugin>
+                        <groupId>org.apache.maven.plugins</groupId>
+                        <artifactId>maven-surefire-plugin</artifactId>
+                        <executions>
+                            <execution>
+                                <phase>integration-test</phase>
+                                <goals>
+                                    <goal>test</goal>
+                                </goals>
+                                <configuration>
+                                    <excludes>
+                                        <exclude>**/*ManualTest.java</exclude>
+                                    </excludes>
+                                    <includes>
+                                        <include>**/*IntegrationTest.java</include>
+                                        <include>**/*IntTest.java</include>
+                                    </includes>
+                                </configuration>
+                            </execution>
+                        </executions>
+                        <configuration>
+                            <systemPropertyVariables>
+                                <test.mime>json</test.mime>
+                            </systemPropertyVariables>
+                        </configuration>
+                    </plugin>
+                    <plugin>
+                        <groupId>org.codehaus.mojo</groupId>
+                        <artifactId>exec-maven-plugin</artifactId>
+                        <version>${exec-maven-plugin.version}</version>
+                        <executions>
+                            <execution>
+                                <id>run-benchmarks</id>
+                                <!-- <phase>integration-test</phase> -->
+                                <phase>none</phase>
+                                <goals>
+                                    <goal>exec</goal>
+                                </goals>
+                                <configuration>
+                                    <classpathScope>test</classpathScope>
+                                    <executable>java</executable>
+                                    <arguments>
+                                        <argument>-classpath</argument>
+                                        <classpath />
+                                        <argument>org.openjdk.jmh.Main</argument>
+                                        <argument>.*</argument>
+                                    </arguments>
+                                </configuration>
+                            </execution>
+                        </executions>
+                    </plugin>
+                </plugins>
+            </build>
+        </profile>
+    </profiles>
+
+    <properties>
+        <maven-javadoc-plugin.version>3.0.0-M1</maven-javadoc-plugin.version>
+        <exec-maven-plugin.version>1.6.0</exec-maven-plugin.version>
+        <source.version>1.8</source.version>
+        <target.version>1.8</target.version>
+    </properties>
+
+</project>

core-java-modules/core-java-console/src/test/java/com/baeldung/asciiart/AsciiArtIntegrationTest.java

@@ -1,10 +1,9 @@
 package com.baeldung.asciiart;
 
-import java.awt.Font;
-
+import com.baeldung.asciiart.AsciiArt.Settings;
 import org.junit.Test;
 
-import com.baeldung.asciiart.AsciiArt.Settings;
+import java.awt.*;
 
 public class AsciiArtIntegrationTest {
 
@@ -16,5 +15,4 @@ public class AsciiArtIntegrationTest {
         
         asciiArt.drawString(text, "*", settings);
     }
-    
 }

core-java-modules/core-java-date-operations-2/README.md

@@ -8,4 +8,5 @@ This module contains articles about date operations in Java.
 - [Converting Java Date to OffsetDateTime](https://www.baeldung.com/java-convert-date-to-offsetdatetime)
 - [How to Set the JVM Time Zone](https://www.baeldung.com/java-jvm-time-zone)
 - [How to determine day of week by passing specific date in Java?](https://www.baeldung.com/java-get-day-of-week)
+- [Finding Leap Years in Java](https://www.baeldung.com/java-leap-year)
 - [[<-- Prev]](/core-java-modules/core-java-date-operations-1)

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

@@ -1,41 +0,0 @@
-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

@@ -1,30 +0,0 @@
-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/GetWeekNumberUnitTest.java

@@ -0,0 +1,64 @@
+package com.baeldung.weeknumber;
+
+import static org.junit.Assert.assertEquals;
+
+import java.time.LocalDate;
+import java.time.temporal.ChronoField;
+import java.time.temporal.WeekFields;
+import java.util.Calendar;
+import java.util.Locale;
+
+import org.junit.Test;
+
+public class GetWeekNumberUnitTest {
+
+    @Test
+    public void givenDateUsingFieldsAndLocaleItaly_whenGetWeekNumber_thenWeekIsReturnedCorrectly() {
+        Calendar calendar = Calendar.getInstance(Locale.ITALY);
+        calendar.set(2020, 10, 22);
+
+        assertEquals(47, calendar.get(Calendar.WEEK_OF_YEAR));
+    }
+
+    @Test
+    public void givenDateUsingFieldsAndLocaleCanada_whenGetWeekNumber_thenWeekIsReturnedCorrectly() {
+        Calendar calendar = Calendar.getInstance(Locale.CANADA);
+        calendar.set(2020, 10, 22);
+
+        assertEquals(48, calendar.get(Calendar.WEEK_OF_YEAR));
+    }
+
+    @Test
+    public void givenDateUsingFieldsAndLocaleItaly_whenChangingWeekCalcSettings_thenWeekIsReturnedCorrectly() {
+        Calendar calendar = Calendar.getInstance();
+        calendar.setFirstDayOfWeek(Calendar.SUNDAY);
+        calendar.setMinimalDaysInFirstWeek(4);
+        calendar.set(2020, 2, 22);
+
+        assertEquals(13, calendar.get(Calendar.WEEK_OF_YEAR));
+    }
+
+    @Test
+    public void givenDateUsingChronoFields_whenGetWeekNumber_thenWeekIsReturnedCorrectly() {
+        LocalDate date = LocalDate.of(2020, 3, 22);
+
+        assertEquals(12, date.get(ChronoField.ALIGNED_WEEK_OF_YEAR));
+    }
+
+    @Test
+    public void givenDateUsingFieldsWithLocaleItaly_whenGetWeekNumber_thenWeekIsReturnedCorrectly() {
+        LocalDate date = LocalDate.of(2020, 3, 22);
+
+        assertEquals(12, date.get(WeekFields.of(Locale.ITALY)
+            .weekOfYear()));
+    }
+
+    @Test
+    public void givenDateUsingFieldsWithLocaleCanada_whenGetWeekNumber_thenWeekIsReturnedCorrectly() {
+        LocalDate date = LocalDate.of(2020, 3, 22);
+
+        assertEquals(13, date.get(WeekFields.of(Locale.CANADA)
+            .weekOfYear()));
+    }
+
+}

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

@@ -1,46 +0,0 @@
-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

@@ -1,49 +0,0 @@
-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/src/test/java/com/baeldung/exceptionininitializererror/ExceptionInInitializerErrorUnitTest.java

@@ -0,0 +1,55 @@
+package com.baeldung.exceptionininitializererror;
+
+import org.junit.Test;
+
+import java.lang.reflect.Constructor;
+
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+public class ExceptionInInitializerErrorUnitTest {
+
+    @Test
+    public void givenStaticVar_whenThrows_thenWrapsItInAnExceptionInInitializerError() {
+        assertThatThrownBy(StaticVar::new)
+          .isInstanceOf(ExceptionInInitializerError.class)
+          .hasCauseInstanceOf(RuntimeException.class);
+    }
+
+    @Test
+    public void givenStaticBlock_whenThrows_thenWrapsItInAnExceptionInInitializerError() {
+        assertThatThrownBy(StaticBlock::new)
+          .isInstanceOf(ExceptionInInitializerError.class)
+          .hasCauseInstanceOf(ArithmeticException.class);
+    }
+
+    private static class CheckedConvention {
+
+        private static Constructor<?> constructor;
+
+        static {
+            try {
+                constructor = CheckedConvention.class.getDeclaredConstructor();
+            } catch (NoSuchMethodException e) {
+                throw new ExceptionInInitializerError(e);
+            }
+        }
+    }
+
+    private static class StaticVar {
+
+        private static int state = initializeState();
+
+        private static int initializeState() {
+            throw new RuntimeException();
+        }
+    }
+
+    private static class StaticBlock {
+
+        private static int state;
+
+        static {
+            state = 42 / 0;
+        }
+    }
+}

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

@@ -0,0 +1,87 @@
+package com.baeldung.exceptions;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.assertFalse;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.AfterEach;
+
+
+public class TooManyOpenFilesExceptionLiveTest {
+
+    //This is not a regular UnitTest due to the fact that it depends on System.gc() to work properly.
+    //As we have to force the JVM to run out of file descriptors, any other tests that uses IO may fail.
+    //This may indirectly affect other tests that are part of the Jenkins Build.
+
+    private File tempFile;
+
+    @BeforeEach
+    public void setUp() throws IOException {
+        tempFile = File.createTempFile("testForException", "tmp");
+    }
+
+    @AfterEach
+    public void tearDown() {
+        //Enforce a GC to clear unreferenced files and release descriptors
+        System.gc();
+        tempFile.delete();
+    }
+
+    @Test
+    public void whenNotClosingResoures_thenIOExceptionShouldBeThrown() {
+        try {
+            for (int x = 0; x < 1000000; x++) {
+                FileInputStream leakyHandle = new FileInputStream(tempFile);
+            }
+            Assertions.fail("Method Should Have Failed");
+        } catch (IOException e) {
+            assertTrue(e.getMessage().toLowerCase().contains("too many open files"));
+        } catch (Exception e) {
+            Assertions.fail("Unexpected exception");
+        }
+    }
+
+    @Test
+    public void whenClosingResoures_thenIOExceptionShouldNotBeThrown() {
+        try {
+            for (int x = 0; x < 1000000; x++) {
+                FileInputStream nonLeakyHandle = null;
+                try {
+                    nonLeakyHandle = new FileInputStream(tempFile);
+                } finally {
+                    if (nonLeakyHandle != null) {
+                        nonLeakyHandle.close();
+                    }
+                }
+            }
+        } catch (IOException e) {
+            assertFalse(e.getMessage().toLowerCase().contains("too many open files"));
+            Assertions.fail("Method Should Not Have Failed");
+        } catch (Exception e) {
+            Assertions.fail("Unexpected exception");
+        }
+    }
+
+    @Test
+    public void whenUsingTryWithResoures_thenIOExceptionShouldNotBeThrown() {
+        try {
+            for (int x = 0; x < 1000000; x++) {
+                try (FileInputStream nonLeakyHandle = new FileInputStream(tempFile)) {
+                    //Do something with the file
+                }
+            }
+        } catch (IOException e) {
+            assertFalse(e.getMessage().toLowerCase().contains("too many open files"));
+            Assertions.fail("Method Should Not Have Failed");
+        } catch (Exception e) {
+            Assertions.fail("Unexpected exception");
+        }
+    }
+}

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

@@ -50,7 +50,7 @@
         <dependency>
             <groupId>com.github.tomakehurst</groupId>
             <artifactId>wiremock</artifactId>
-            <version>2.26.3</version>
+            <version>${wiremock.version}</version>
             <scope>test</scope>
         </dependency>
 
@@ -80,6 +80,7 @@
     <properties>
         <assertj.version>3.6.1</assertj.version>
         <maven-javadoc-plugin.version>3.0.0-M1</maven-javadoc-plugin.version>
+        <wiremock.version>2.26.3</wiremock.version>
     </properties>
 
 </project>

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

@@ -5,4 +5,5 @@ 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 – Write an InputStream to a File](https://www.baeldung.com/convert-input-stream-to-a-file)
+- [Converting a BufferedReader to a JSONObject](https://www.baeldung.com/java-bufferedreader-to-jsonobject)
 - More articles: [[<-- prev]](/core-java-modules/core-java-io-conversions)

core-java-modules/core-java-io-conversions-2/pom.xml

@@ -21,6 +21,11 @@
             <artifactId>commons-lang3</artifactId>
             <version>${commons-lang3.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.json</groupId>
+            <artifactId>json</artifactId>
+            <version>${json.version}</version>
+        </dependency>
     </dependencies>
 
     <build>
@@ -33,4 +38,8 @@
         </resources>
     </build>
 
+    <properties>
+        <json.version>20200518</json.version>
+    </properties>
+
 </project>

core-java-modules/core-java-io-conversions-2/src/test/java/com/baeldung/bufferedreadertojsonobject/JavaBufferedReaderToJSONObjectUnitTest.java

@@ -0,0 +1,48 @@
+package com.baeldung.bufferedreadertojsonobject;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+import java.io.BufferedReader;
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
+
+import org.json.JSONObject;
+import org.json.JSONTokener;
+import org.junit.Test;
+
+public class JavaBufferedReaderToJSONObjectUnitTest {
+
+    @Test
+    public void givenValidJson_whenUsingBufferedReader_thenJSONTokenerConverts() {
+        byte[] b = "{ \"name\" : \"John\", \"age\" : 18 }".getBytes(StandardCharsets.UTF_8);
+        InputStream is = new ByteArrayInputStream(b);
+        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));
+        JSONTokener tokener = new JSONTokener(bufferedReader);
+        JSONObject json = new JSONObject(tokener);
+
+        assertNotNull(json);
+        assertEquals("John", json.get("name"));
+        assertEquals(18, json.get("age"));
+    }
+
+    @Test
+    public void givenValidJson_whenUsingString_thenJSONObjectConverts() throws IOException {
+        byte[] b = "{ \"name\" : \"John\", \"age\" : 18 }".getBytes(StandardCharsets.UTF_8);
+        InputStream is = new ByteArrayInputStream(b);
+        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));
+        StringBuilder sb = new StringBuilder();
+        String line;
+        while ((line = bufferedReader.readLine()) != null) {
+            sb.append(line);
+        }
+        JSONObject json = new JSONObject(sb.toString());
+
+        assertNotNull(json);
+        assertEquals("John", json.get("name"));
+        assertEquals(18, json.get("age"));
+    }
+}

core-java-modules/core-java-io/src/test/java/com/baeldung/size/JavaFolderSizeUnitTest.java

@@ -72,7 +72,7 @@ public class JavaFolderSizeUnitTest {
     public void whenGetFolderSizeUsingGuava_thenCorrect() {
         final File folder = new File(path);
 
-        final Iterable<File> files = com.google.common.io.Files.fileTreeTraverser().breadthFirstTraversal(folder);
+        final Iterable<File> files = com.google.common.io.Files.fileTraverser().breadthFirst(folder);
         final long size = StreamSupport.stream(files.spliterator(), false).filter(File::isFile).mapToLong(File::length).sum();
 
         assertEquals(EXPECTED_SIZE, size);

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

@@ -0,0 +1,5 @@
+## Core Java JVM Cookbooks and Examples
+
+This module contains articles about working with the Java Virtual Machine (JVM).
+
+### Relevant Articles: 

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

@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-jvm-2</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-jvm-2</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>${junit.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jol</groupId>
+            <artifactId>jol-core</artifactId>
+            <version>${jol-core.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <assertj.version>3.6.1</assertj.version>
+        <jol-core.version>0.10</jol-core.version>
+    </properties>
+
+</project>

core-java-modules/core-java-jvm-2/src/test/java/com/baeldung/arraylength/ArrayLengthUnitTest.java

@@ -0,0 +1,13 @@
+package com.baeldung.arraylength;
+
+import org.junit.Test;
+import org.openjdk.jol.info.ClassLayout;
+
+public class ArrayLengthUnitTest {
+
+    @Test
+    public void printingTheArrayLength() {
+        int[] ints = new int[42];
+        System.out.println(ClassLayout.parseInstance(ints).toPrintable());
+    }
+}

core-java-modules/core-java-jvm-2/src/test/java/com/baeldung/memlayout/MemoryLayoutUnitTest.java

@@ -0,0 +1,108 @@
+package com.baeldung.memlayout;
+
+import org.junit.Test;
+import org.openjdk.jol.info.ClassLayout;
+import org.openjdk.jol.vm.VM;
+import sun.misc.Contended;
+
+public class MemoryLayoutUnitTest {
+
+    private volatile Object consumer;
+
+    @Test
+    public void printingTheVMDetails() {
+        System.out.println(VM.current().details());
+    }
+
+    @Test
+    public void simpleMemoryLayout() {
+        System.out.println(ClassLayout.parseClass(SimpleInt.class).toPrintable());
+    }
+
+    @Test
+    public void identityHashCodeMemoryLayout() {
+        SimpleInt instance = new SimpleInt();
+        System.out.println(ClassLayout.parseInstance(instance).toPrintable());
+
+        System.out.println("The identity hash code is " + System.identityHashCode(instance));
+        System.out.println(ClassLayout.parseInstance(instance).toPrintable());
+    }
+
+    @Test
+    public void alignmentMemoryLayout() {
+        System.out.println(ClassLayout.parseClass(SimpleLong.class).toPrintable());
+    }
+
+    @Test
+    public void fieldPackingMemoryLayout() {
+        System.out.println(ClassLayout.parseClass(FieldsArrangement.class).toPrintable());
+    }
+
+    @Test
+    public void monitorLockMemoryLayout() {
+        Lock lock = new Lock();
+        System.out.println(ClassLayout.parseInstance(lock).toPrintable());
+
+        synchronized (lock) {
+            System.out.println(ClassLayout.parseInstance(lock).toPrintable());
+        }
+    }
+
+    @Test
+    public void ageAndTenuringMemoryLayout() {
+        Object instance = new Object();
+        long lastAddr = VM.current().addressOf(instance);
+        ClassLayout layout = ClassLayout.parseInstance(instance);
+
+        for (int i = 0; i < 10_000; i++) {
+            long currentAddr = VM.current().addressOf(instance);
+            if (currentAddr != lastAddr) {
+                System.out.println(layout.toPrintable());
+            }
+
+            for (int j = 0; j < 10_000; j++) {
+                consumer = new Object();
+            }
+
+            lastAddr = currentAddr;
+        }
+    }
+
+    @Test
+    public void contendedMemoryLayout() {
+        System.out.println(ClassLayout.parseClass(Isolated.class).toPrintable());
+    }
+
+    @Test
+    public void arrayMemoryLayout() {
+        boolean[] booleans = new boolean[3];
+        System.out.println(ClassLayout.parseInstance(booleans).toPrintable());
+    }
+
+    private static class SimpleInt {
+        private int state;
+    }
+
+    private static class SimpleLong {
+        private long state;
+    }
+
+    private static class FieldsArrangement {
+        private boolean first;
+        private char second;
+        private double third;
+        private int fourth;
+        private boolean fifth;
+    }
+
+    private static class Lock {}
+
+    private static class Isolated {
+
+        @Contended
+        private int i;
+
+        @Contended
+        private long l;
+    }
+}

core-java-modules/core-java-jvm-2/src/test/java/com/baeldung/objectsize/Course.java

@@ -0,0 +1,10 @@
+package com.baeldung.objectsize;
+
+public class Course {
+
+    private String name;
+
+    public Course(String name) {
+        this.name = name;
+    }
+}

core-java-modules/core-java-jvm-2/src/test/java/com/baeldung/objectsize/InstrumentedSize.java

@@ -0,0 +1,11 @@
+package com.baeldung.objectsize;
+
+public class InstrumentedSize {
+
+    public static void main(String[] args) {
+        String ds = "Data Structures";
+        Course course = new Course(ds);
+
+        System.out.println(ObjectSizeCalculator.sizeOf(course));
+    }
+}

core-java-modules/core-java-jvm-2/src/test/java/com/baeldung/objectsize/MANIFEST.MF

@@ -0,0 +1 @@
+Premain-Class: com.baeldung.objectsize.ObjectSizeCalculator

core-java-modules/core-java-jvm-2/src/test/java/com/baeldung/objectsize/ObjectSizeCalculator.java

@@ -0,0 +1,16 @@
+package com.baeldung.objectsize;
+
+import java.lang.instrument.Instrumentation;
+
+public class ObjectSizeCalculator {
+
+    private static Instrumentation instrumentation;
+
+    public static void premain(String args, Instrumentation inst) {
+        instrumentation = inst;
+    }
+
+    public static long sizeOf(Object o) {
+        return instrumentation.getObjectSize(o);
+    }
+}

core-java-modules/core-java-jvm-2/src/test/java/com/baeldung/objectsize/ObjectSizeUnitTest.java

@@ -0,0 +1,40 @@
+package com.baeldung.objectsize;
+
+import org.junit.Test;
+import org.openjdk.jol.info.ClassLayout;
+import org.openjdk.jol.info.GraphLayout;
+import org.openjdk.jol.vm.VM;
+
+public class ObjectSizeUnitTest {
+
+    @Test
+    public void printingTheVMDetails() {
+        System.out.println(VM.current().details());
+    }
+
+    @Test
+    public void printingTheProfClassLayout() {
+        System.out.println(ClassLayout.parseClass(Professor.class).toPrintable());
+    }
+
+    @Test
+    public void printingTheCourseClassLayout() {
+        System.out.println(ClassLayout.parseClass(Course.class).toPrintable());
+    }
+
+    @Test
+    public void printingACourseInstanceLayout() {
+        String ds = "Data Structures";
+        Course course = new Course(ds);
+
+        System.out.println("The shallow size is :" + VM.current().sizeOf(course));
+
+        System.out.println(ClassLayout.parseInstance(course).toPrintable());
+        System.out.println(ClassLayout.parseInstance(ds).toPrintable());
+        System.out.println(ClassLayout.parseInstance(ds.toCharArray()).toPrintable());
+
+        System.out.println(GraphLayout.parseInstance(course).totalSize());
+        System.out.println(GraphLayout.parseInstance(course).toFootprint());
+        System.out.println(GraphLayout.parseInstance(course).toPrintable());
+    }
+}

core-java-modules/core-java-jvm-2/src/test/java/com/baeldung/objectsize/Professor.java

@@ -0,0 +1,24 @@
+package com.baeldung.objectsize;
+
+import java.time.LocalDate;
+import java.util.List;
+
+public class Professor {
+
+    private String name;
+    private boolean tenured;
+    private List<Course> courses;
+    private int level;
+    private LocalDate birthDay;
+    private double lastEvaluation;
+
+    public Professor(String name, boolean tenured, List<Course> courses,
+      int level, LocalDate birthDay, double lastEvaluation) {
+        this.name = name;
+        this.tenured = tenured;
+        this.courses = courses;
+        this.level = level;
+        this.birthDay = birthDay;
+        this.lastEvaluation = lastEvaluation;
+    }
+}

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

@@ -12,3 +12,7 @@ This module contains articles about working with the Java Virtual Machine (JVM).
 - [Guide to System.gc()](https://www.baeldung.com/java-system-gc)
 - [Runtime.getRuntime().halt() vs System.exit() in Java](https://www.baeldung.com/java-runtime-halt-vs-system-exit)
 - [Adding Shutdown Hooks for JVM Applications](https://www.baeldung.com/jvm-shutdown-hooks)
+- [How to Get the Size of an Object in Java](http://www.baeldung.com/java-size-of-object)
+- [What Causes java.lang.OutOfMemoryError: unable to create new native thread](https://www.baeldung.com/java-outofmemoryerror-unable-to-create-new-native-thread)
+- [View Bytecode of a Class File in Java](https://www.baeldung.com/java-class-view-bytecode)
+- [boolean and boolean[] Memory Layout in the JVM](https://www.baeldung.com/jvm-boolean-memory-layout)

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

@@ -51,14 +51,37 @@
             <scope>system</scope>
             <systemPath>${java.home}/../lib/tools.jar</systemPath>
         </dependency>
+        <dependency>
+            <groupId>org.ow2.asm</groupId>
+            <artifactId>asm</artifactId>
+            <version>${asm.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.ow2.asm</groupId>
+            <artifactId>asm-util</artifactId>
+            <version>${asm.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.bcel</groupId>
+            <artifactId>bcel</artifactId>
+            <version>${bcel.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jol</groupId>
+            <artifactId>jol-core</artifactId>
+            <version>${jol-core.version}</version>
+        </dependency>
     </dependencies>
 
     <properties>
         <assertj.version>3.6.1</assertj.version>
         <!-- instrumentation -->
-        <javaassist.version>3.21.0-GA</javaassist.version>
+        <javaassist.version>3.27.0-GA</javaassist.version>
         <esapi.version>2.1.0.1</esapi.version>
         <sun.tools.version>1.8.0</sun.tools.version>
+        <jol-core.version>0.10</jol-core.version>
+        <asm.version>8.0.1</asm.version>
+        <bcel.version>6.5.0</bcel.version>
     </properties>
 
 </project>

core-java-modules/core-java-jvm/src/test/java/com/baeldung/boolsize/BooleanSizeUnitTest.java

@@ -0,0 +1,25 @@
+package com.baeldung.boolsize;
+
+import org.junit.Test;
+import org.openjdk.jol.info.ClassLayout;
+import org.openjdk.jol.vm.VM;
+
+public class BooleanSizeUnitTest {
+
+    @Test
+    public void printingTheVMDetails() {
+        System.out.println(VM.current().details());
+    }
+
+    @Test
+    public void printingTheBoolWrapper() {
+        System.out.println(ClassLayout.parseClass(BooleanWrapper.class).toPrintable());
+    }
+
+    @Test
+    public void printingTheBoolArray() {
+        boolean[] value = new boolean[3];
+
+        System.out.println(ClassLayout.parseInstance(value).toPrintable());
+    }
+}

core-java-modules/core-java-jvm/src/test/java/com/baeldung/boolsize/BooleanWrapper.java

@@ -0,0 +1,5 @@
+package com.baeldung.boolsize;
+
+class BooleanWrapper {
+    private boolean value;
+}

core-java-modules/core-java-jvm/src/test/java/com/baeldung/bytecode/ViewBytecodeUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.bytecode;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.io.StringWriter;
+
+import org.apache.bcel.Repository;
+import org.apache.bcel.classfile.JavaClass;
+import org.junit.Test;
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.util.TraceClassVisitor;
+import javassist.ClassPool;
+import javassist.NotFoundException;
+import javassist.bytecode.ClassFile;
+
+public class ViewBytecodeUnitTest {
+    
+    @Test
+    public void whenUsingASM_thenReadBytecode() throws IOException {
+        ClassReader reader = new ClassReader("java.lang.Object");
+        StringWriter sw = new StringWriter();
+        TraceClassVisitor tcv = new TraceClassVisitor(new PrintWriter(sw));
+        reader.accept(tcv, 0); 
+        
+        assertTrue(sw.toString().contains("public class java/lang/Object")); 
+    }
+    
+    @Test
+    public void whenUsingBCEL_thenReadBytecode() throws ClassNotFoundException {
+        JavaClass objectClazz = Repository.lookupClass("java.lang.Object");
+        
+        assertEquals(objectClazz.getClassName(), "java.lang.Object");   
+        assertEquals(objectClazz.getMethods().length, 14);
+        assertTrue(objectClazz.toString().contains("public class java.lang.Object"));
+    }
+    
+    @Test
+    public void whenUsingJavassist_thenReadBytecode() throws NotFoundException {
+        ClassPool cp = ClassPool.getDefault();
+        ClassFile cf = cp.get("java.lang.Object").getClassFile();
+        
+        assertEquals(cf.getName(), "java.lang.Object");
+        assertEquals(cf.getMethods().size(), 14);
+    }
+    
+}
+
+

core-java-modules/core-java-jvm/src/test/java/com/baeldung/error/oom/ExecutorServiceUnitTest.java

@@ -0,0 +1,40 @@
+package com.baeldung.error.oom;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+import java.util.stream.IntStream;
+
+import org.junit.jupiter.api.Test;
+
+public class ExecutorServiceUnitTest {
+
+    @Test
+    public void givenAnExecutorService_WhenMoreTasksSubmitted_ThenAdditionalTasksWait() {
+
+        // Given
+        int noOfThreads = 5;
+        ExecutorService executorService = Executors.newFixedThreadPool(noOfThreads);
+
+        Runnable runnableTask = () -> {
+            try {
+                TimeUnit.HOURS.sleep(1);
+            } catch (InterruptedException e) {
+                e.printStackTrace();
+            }
+        };
+
+        // When
+        IntStream.rangeClosed(1, 10)
+            .forEach(i -> executorService.submit(runnableTask));
+
+        // Then
+        assertThat(((ThreadPoolExecutor) executorService).getQueue()
+            .size(), is(equalTo(5)));
+    }
+}

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

@@ -11,4 +11,6 @@ This module contains articles about core features in the Java language
 - [Guide to the Java finally Keyword](https://www.baeldung.com/java-finally-keyword)
 - [The Java Headless Mode](https://www.baeldung.com/java-headless-mode)
 - [Comparing Long Values in Java](https://www.baeldung.com/java-compare-long-values)
+- [Comparing Objects in Java](https://www.baeldung.com/java-comparing-objects)
+- [Casting int to Enum in Java](https://www.baeldung.com/java-cast-int-to-enum)
 - [[<-- Prev]](/core-java-modules/core-java-lang)

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

@@ -22,15 +22,15 @@ public class PersonWithEquals {
         this.birthDate = birthDate;
     }
 
-    public String firstName() {
+    public String getFirstName() {
         return firstName;
     }
 
-    public String lastName() {
+    public String getLastName() {
         return lastName;
     }
 
-    public LocalDate birthDate() {
+    public LocalDate getBirthDate() {
         return birthDate;
     }
 

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

@@ -22,6 +22,18 @@ public class PersonWithEqualsAndComparable implements Comparable<PersonWithEqual
         this.birthDate = birthDate;
     }
 
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public LocalDate getBirthDate() {
+        return birthDate;
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

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

@@ -23,15 +23,15 @@ public class PersonWithEqualsAndComparableUsingComparator implements Comparable<
         this.birthDate = birthDate;
     }
 
-    public String firstName() {
+    public String getFirstName() {
         return firstName;
     }
 
-    public String lastName() {
+    public String getLastName() {
         return lastName;
     }
 
-    public LocalDate birthDate() {
+    public LocalDate getBirthDate() {
         return birthDate;
     }
 
@@ -52,9 +52,9 @@ public class PersonWithEqualsAndComparableUsingComparator implements Comparable<
 
     @Override
     public int compareTo(PersonWithEqualsAndComparableUsingComparator o) {
-        return Comparator.comparing(PersonWithEqualsAndComparableUsingComparator::lastName)
-          .thenComparing(PersonWithEqualsAndComparableUsingComparator::firstName)
-          .thenComparing(PersonWithEqualsAndComparableUsingComparator::birthDate, Comparator.nullsLast(Comparator.naturalOrder()))
+        return Comparator.comparing(PersonWithEqualsAndComparableUsingComparator::getLastName)
+          .thenComparing(PersonWithEqualsAndComparableUsingComparator::getFirstName)
+          .thenComparing(PersonWithEqualsAndComparableUsingComparator::getBirthDate, Comparator.nullsLast(Comparator.naturalOrder()))
           .compare(this, o);
     }
 }

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

@@ -22,6 +22,18 @@ public class PersonWithEqualsAndWrongComparable implements Comparable<PersonWith
         this.birthDate = birthDate;
     }
 
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public LocalDate getBirthDate() {
+        return birthDate;
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

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

@@ -8,4 +8,12 @@ public class PersonWithoutEquals {
         this.firstName = firstName;
         this.lastName = lastName;
     }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
 }

core-java-modules/core-java-lang-2/src/main/java/com/baeldung/inttoenum/PizzaStatus.java

@@ -21,11 +21,10 @@ public enum PizzaStatus {
     private static Map<Integer, PizzaStatus> timeToDeliveryToEnumValuesMapping = new HashMap<>();
 
     static {
-        PizzaStatus[] pizzaStatuses = PizzaStatus.values();
-        for (int pizzaStatusIndex = 0; pizzaStatusIndex < pizzaStatuses.length; pizzaStatusIndex++) {
+        for (PizzaStatus pizzaStatus : PizzaStatus.values()) {
             timeToDeliveryToEnumValuesMapping.put(
-                pizzaStatuses[pizzaStatusIndex].getTimeToDelivery(),
-                pizzaStatuses[pizzaStatusIndex]
+                    pizzaStatus.getTimeToDelivery(),
+                    pizzaStatus
             );
         }
     }

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

@@ -20,7 +20,7 @@ class ComparatorInterfaceUnitTest {
         Comparator<PersonWithEquals> compareByFirstNames = new Comparator<PersonWithEquals>() {
             @Override
             public int compare(PersonWithEquals o1, PersonWithEquals o2) {
-                return o1.firstName().compareTo(o2.firstName());
+                return o1.getFirstName().compareTo(o2.getFirstName());
             }
         };
         people.sort(compareByFirstNames);
@@ -37,7 +37,7 @@ class ComparatorInterfaceUnitTest {
         people.add(joe);
         people.add(allan);
 
-        Comparator<PersonWithEquals> compareByFirstNames = Comparator.comparing(PersonWithEquals::firstName);
+        Comparator<PersonWithEquals> compareByFirstNames = Comparator.comparing(PersonWithEquals::getFirstName);
         people.sort(compareByFirstNames);
 
         assertThat(people).containsExactly(allan, joe);

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

@@ -63,8 +63,8 @@ class GuavaUnitTest {
             PersonWithEquals joe = new PersonWithEquals("Joe", "Portman");
 
             int comparisonResult = ComparisonChain.start()
-              .compare(natalie.lastName(), joe.lastName())
-              .compare(natalie.firstName(), joe.firstName())
+              .compare(natalie.getLastName(), joe.getLastName())
+              .compare(natalie.getFirstName(), joe.getFirstName())
               .result();
 
             assertThat(comparisonResult).isPositive();

core-java-modules/core-java-lang-2/src/test/java/com/baeldung/inttoenum/IntToEnumUnitTest.java

@@ -1,7 +1,12 @@
 package com.baeldung.inttoenum;
 
+import org.assertj.core.api.Assertions;
 import org.junit.Test;
 
+import java.util.Arrays;
+import java.util.Optional;
+
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.assertEquals;
 
 public class IntToEnumUnitTest {
@@ -9,19 +14,33 @@ public class IntToEnumUnitTest {
     @Test
     public void whenIntToEnumUsingValuesMethod_thenReturnEnumObject() {
         int timeToDeliveryForOrderedPizzaStatus = 5;
-        PizzaStatus[] pizzaStatuses = PizzaStatus.values();
+
         PizzaStatus pizzaOrderedStatus = null;
-        for (int pizzaStatusIndex = 0; pizzaStatusIndex < pizzaStatuses.length; pizzaStatusIndex++) {
-            if (pizzaStatuses[pizzaStatusIndex].getTimeToDelivery() == timeToDeliveryForOrderedPizzaStatus) {
-                pizzaOrderedStatus = pizzaStatuses[pizzaStatusIndex];
+
+        for (PizzaStatus pizzaStatus : PizzaStatus.values()) {
+            if (pizzaStatus.getTimeToDelivery() == timeToDeliveryForOrderedPizzaStatus) {
+                pizzaOrderedStatus = pizzaStatus;
             }
         }
-        assertEquals(pizzaOrderedStatus, PizzaStatus.ORDERED);
+
+        assertThat(pizzaOrderedStatus).isEqualTo(PizzaStatus.ORDERED);
     }
 
     @Test
     public void whenIntToEnumUsingMap_thenReturnEnumObject() {
         int timeToDeliveryForOrderedPizzaStatus = 5;
-        assertEquals(PizzaStatus.castIntToEnum(timeToDeliveryForOrderedPizzaStatus), PizzaStatus.ORDERED);
+
+        assertThat(PizzaStatus.castIntToEnum(timeToDeliveryForOrderedPizzaStatus)).isEqualTo(PizzaStatus.ORDERED);
+    }
+
+    @Test
+    public void whenIntToEnumUsingStream_thenReturnEnumObject() {
+        int timeToDeliveryForOrderedPizzaStatus = 5;
+
+        Optional<PizzaStatus> pizzaStatus = Arrays.stream(PizzaStatus.values())
+          .filter(p -> p.getTimeToDelivery() == timeToDeliveryForOrderedPizzaStatus)
+          .findFirst();
+
+        assertThat(pizzaStatus).hasValue(PizzaStatus.ORDERED);
     }
 }

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

@@ -0,0 +1,6 @@
+## Core Java Lang (Part 3)
+
+This module contains articles about core features in the Java language
+
+### Relevant Articles: 
+- [[<-- Prev]](/core-java-modules/core-java-lang-2)

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

@@ -0,0 +1,36 @@
+<?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-3</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-lang-3</name>
+    <packaging>jar</packaging>
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../</relativePath>
+    </parent>
+
+    <dependencies>
+        
+    </dependencies>
+
+    <build>
+        <finalName>core-java-lang-3</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <properties>
+        
+    </properties>
+
+</project>

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/isinstancevsisassignablefrom/IsoscelesTriangle.java

@@ -0,0 +1,5 @@
+package com.baeldung.isinstancevsisassignablefrom;
+
+public class IsoscelesTriangle extends Triangle {
+
+}

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/isinstancevsisassignablefrom/Shape.java

@@ -0,0 +1,5 @@
+package com.baeldung.isinstancevsisassignablefrom;
+
+public interface Shape {
+
+}

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/isinstancevsisassignablefrom/Triangle.java

@@ -0,0 +1,5 @@
+package com.baeldung.isinstancevsisassignablefrom;
+
+public class Triangle implements Shape {
+
+}

core-java-modules/core-java-lang-3/src/test/java/com/baeldung/isinstancevsisassignablefrom/IsInstanceIsAssignableFromUnitTest.java

@@ -0,0 +1,67 @@
+package com.baeldung.isinstancevsisassignablefrom;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class IsInstanceIsAssignableFromUnitTest {
+    
+    @Test
+    public void whenUsingIsInstanceProperly_desiredResultsHappen() {
+        Shape shape = new Triangle();
+        Triangle triangle = new Triangle();
+        IsoscelesTriangle isoscelesTriangle = new IsoscelesTriangle();
+        Triangle isoscelesTriangle2 = new IsoscelesTriangle();
+        Shape nonspecificShape = null;
+        
+        assertTrue(Shape.class.isInstance(shape));
+        assertTrue(Shape.class.isInstance(triangle));
+        assertTrue(Shape.class.isInstance(isoscelesTriangle));
+        assertTrue(Shape.class.isInstance(isoscelesTriangle2));
+        assertFalse(Shape.class.isInstance(nonspecificShape));
+        
+        assertTrue(Triangle.class.isInstance(shape));
+        assertTrue(Triangle.class.isInstance(triangle));
+        assertTrue(Triangle.class.isInstance(isoscelesTriangle));
+        assertTrue(Triangle.class.isInstance(isoscelesTriangle2));
+        
+        assertFalse(IsoscelesTriangle.class.isInstance(shape));
+        assertFalse(IsoscelesTriangle.class.isInstance(triangle));
+        assertTrue(IsoscelesTriangle.class.isInstance(isoscelesTriangle));
+        assertTrue(IsoscelesTriangle.class.isInstance(isoscelesTriangle2));        
+    }
+    
+    @Test
+    public void whenUsingIsAssignableFromProperly_desiredResultsHappen() {
+        Shape shape = new Triangle();
+        Triangle triangle = new Triangle();
+        IsoscelesTriangle isoscelesTriangle = new IsoscelesTriangle();
+        Triangle isoscelesTriangle2 = new IsoscelesTriangle();
+        
+        assertFalse(shape.getClass().isAssignableFrom(Shape.class));
+        assertTrue(shape.getClass().isAssignableFrom(shape.getClass()));
+        assertTrue(shape.getClass().isAssignableFrom(triangle.getClass()));
+        assertTrue(shape.getClass().isAssignableFrom(isoscelesTriangle.getClass()));
+        assertTrue(shape.getClass().isAssignableFrom(isoscelesTriangle2.getClass()));
+        
+        assertFalse(triangle.getClass().isAssignableFrom(Shape.class));
+        assertTrue(triangle.getClass().isAssignableFrom(shape.getClass()));
+        assertTrue(triangle.getClass().isAssignableFrom(triangle.getClass()));
+        assertTrue(triangle.getClass().isAssignableFrom(isoscelesTriangle.getClass()));
+        assertTrue(triangle.getClass().isAssignableFrom(isoscelesTriangle2.getClass()));
+        
+        assertFalse(isoscelesTriangle.getClass().isAssignableFrom(Shape.class));
+        assertFalse(isoscelesTriangle.getClass().isAssignableFrom(shape.getClass()));
+        assertFalse(isoscelesTriangle.getClass().isAssignableFrom(triangle.getClass()));
+        assertTrue(isoscelesTriangle.getClass().isAssignableFrom(isoscelesTriangle.getClass()));
+        assertTrue(isoscelesTriangle.getClass().isAssignableFrom(isoscelesTriangle2.getClass()));
+        
+        assertFalse(isoscelesTriangle2.getClass().isAssignableFrom(Shape.class));
+        assertFalse(isoscelesTriangle2.getClass().isAssignableFrom(shape.getClass()));
+        assertFalse(isoscelesTriangle2.getClass().isAssignableFrom(triangle.getClass()));
+        assertTrue(isoscelesTriangle2.getClass().isAssignableFrom(isoscelesTriangle.getClass()));
+        assertTrue(isoscelesTriangle2.getClass().isAssignableFrom(isoscelesTriangle2.getClass()));
+    }
+
+}

core-java-modules/core-java-lang-math/README.md

@@ -6,7 +6,6 @@
 - [Java 8 Math New Methods](https://www.baeldung.com/java-8-math)
 - [Java 8 Unsigned Arithmetic Support](https://www.baeldung.com/java-unsigned-arithmetic)
 - [How to Separate Double into Integer and Decimal Parts](https://www.baeldung.com/java-separate-double-into-integer-decimal-parts)
-- [The strictfp Keyword in Java](https://www.baeldung.com/java-strictfp)
 - [Basic Calculator in Java](https://www.baeldung.com/java-basic-calculator)
 - [Overflow and Underflow in Java](https://www.baeldung.com/java-overflow-underflow)
 - [Obtaining a Power Set of a Set in Java](https://www.baeldung.com/java-power-set-of-a-set)

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

@@ -6,3 +6,4 @@ This module contains articles about generics in Java
 - [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)
+- [Super Type Tokens in Java Generics](https://www.baeldung.com/java-super-type-tokens)

core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/covariance/IntegerProducer.java

@@ -0,0 +1,8 @@
+package com.baeldung.covariance;
+
+public class IntegerProducer extends Producer {
+    @Override
+    public Integer produce(String input) {
+        return Integer.parseInt(input);
+    }
+}