Merge pull request #1 from eugenp/master

Merge

akka-http/pom.xml

@@ -38,8 +38,6 @@
     </dependencies>
 
     <properties>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <akka.http.version>10.0.11</akka.http.version>
         <akka.stream.version>2.5.11</akka.stream.version>
     </properties>

algorithms-miscellaneous-3/pom.xml

@@ -91,8 +91,6 @@
         <commons-collections4.version>4.3</commons-collections4.version>
         <guava.version>28.0-jre</guava.version>
         <retrofit.version>2.6.0</retrofit.version>
-        <jmh-core.version>1.19</jmh-core.version>
-        <jmh-generator.version>1.19</jmh-generator.version>
         <commons.lang3.version>3.8.1</commons.lang3.version>
         <JUnitParams.version>1.1.0</JUnitParams.version>
     </properties>

algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/maximumsubarray/KadaneAlgorithm.java

@@ -13,22 +13,22 @@ public class KadaneAlgorithm {
         int start = 0;
         int end = 0;
 
-        int maxSoFar = 0, maxEndingHere = 0;
+        int maxSoFar = arr[0], maxEndingHere = arr[0];
-
         for (int i = 0; i < size; i++) {
 
             if (arr[i] > maxEndingHere + arr[i]) {
                 start = i;
                 maxEndingHere = arr[i];
-            } else
+            } else {
                 maxEndingHere = maxEndingHere + arr[i];
+            }
 
             if (maxSoFar < maxEndingHere) {
                 maxSoFar = maxEndingHere;
                 end = i;
             }
         }
-        logger.info("Found Maximum Subarray between {} and {}", start, end);
+        logger.info("Found Maximum Subarray between {} and {}", Math.min(start, end), end);
         return maxSoFar;
     }
 }

algorithms-miscellaneous-5/src/test/java/com/baeldung/algorithms/maximumsubarray/KadaneAlgorithmUnitTest.java

@@ -9,11 +9,22 @@ class KadaneAlgorithmUnitTest {
     @Test
     void givenArrayWithNegativeNumberWhenMaximumSubarrayThenReturns6() {
         //given
-        int[] arr = new int[]{-3, 1, -8, 4, -1, 2, 1, -5, 5};
+        int[] arr = new int[] { -3, 1, -8, 4, -1, 2, 1, -5, 5 };
         //when
         KadaneAlgorithm algorithm = new KadaneAlgorithm();
         int maxSum = algorithm.maxSubArraySum(arr);
         //then
         assertEquals(6, maxSum);
     }
+
+    @Test
+    void givenArrayWithAllNegativeNumbersWhenMaximumSubarrayThenReturnsExpectedResult() {
+        //given
+        int[] arr = new int[] { -8, -7, -5, -4, -3, -1, -2 };
+        //when
+        KadaneAlgorithm algorithm = new KadaneAlgorithm();
+        int maxSum = algorithm.maxSubArraySum(arr);
+        //then
+        assertEquals(-1, maxSum);
+    }
 }

apache-libraries/src/test/java/com/baeldung/avro/util/serealization/AvroSerealizerDeSerealizerIntegrationTest.java

@@ -13,7 +13,7 @@ import java.util.Objects;
 
 import static org.junit.Assert.*;
 
-public class AvroSerealizerDeSerealizerUnitTest {
+public class AvroSerealizerDeSerealizerIntegrationTest {
 
     AvroSerealizer serealizer;
     AvroDeSerealizer deSerealizer;

apache-libraries/src/test/java/com/baeldung/meecrowave/ArticleEndpointsIntegrationTest.java

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

apache-poi/README.md

@@ -11,3 +11,4 @@ This module contains articles about Apache POI
 - [Get String Value of Excel Cell with Apache POI](https://www.baeldung.com/java-apache-poi-cell-string-value)
 - [Read Excel Cell Value Rather Than Formula With Apache POI](https://www.baeldung.com/apache-poi-read-cell-value-formula)
 - [Setting Formulas in Excel with Apache POI](https://www.baeldung.com/java-apache-poi-set-formulas)
+- [Insert a Row in Excel Using Apache POI](https://www.baeldung.com/apache-poi-insert-excel-row)

aws-reactive/pom.xml

@@ -100,7 +100,6 @@
     </build>
 
     <properties>
-        <java.version>1.8</java.version>
         <spring.version>2.2.1.RELEASE</spring.version>
         <awssdk.version>2.10.27</awssdk.version>
     </properties>

core-groovy-2/pom.xml

@@ -115,7 +115,6 @@
             </plugin>
             <plugin>
                 <artifactId>maven-surefire-plugin</artifactId>
-                <version>${surefire.plugin.version}</version>
                 <configuration>
                     <useFile>false</useFile>
                     <includes>
@@ -186,7 +185,6 @@
         <logback.version>1.2.3</logback.version>
         <groovy.version>2.5.7</groovy.version>
         <assembly.plugin.version>3.1.0</assembly.plugin.version>
-        <surefire.plugin.version>2.20.1</surefire.plugin.version>
         <compiler.plugin.version>3.8.0</compiler.plugin.version>
         <groovy.compiler.version>3.3.0-01</groovy.compiler.version>
     </properties>

core-groovy-collections/pom.xml

@@ -101,7 +101,6 @@
             </plugin>
             <plugin>
                 <artifactId>maven-surefire-plugin</artifactId>
-                <version>${surefire.plugin.version}</version>
                 <configuration>
                     <useFile>false</useFile>
                     <includes>
@@ -128,7 +127,6 @@
         <hsqldb.version>2.4.0</hsqldb.version>
         <spock-core.version>1.1-groovy-2.4</spock-core.version>
         <gmavenplus-plugin.version>1.6</gmavenplus-plugin.version>
-        <surefire.plugin.version>2.20.1</surefire.plugin.version>
     </properties>
 
 </project>

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

@@ -11,3 +11,4 @@ This module contains articles about Java 10 core features
 - [Copying Sets in Java](https://www.baeldung.com/java-copy-sets)
 - [Converting between a List and a Set in Java](https://www.baeldung.com/convert-list-to-set-and-set-to-list)
 - [Java IndexOutOfBoundsException “Source Does Not Fit in Dest”](https://www.baeldung.com/java-indexoutofboundsexception)
+- [Collect a Java Stream to an Immutable Collection](https://www.baeldung.com/java-stream-immutable-collection)

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

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

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

@@ -32,12 +32,12 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-core.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-generator.version}</version>
             <scope>provided</scope>
         </dependency>
         <dependency>
@@ -105,7 +105,6 @@
         <guava.version>27.1-jre</guava.version>
         <assertj.version>3.11.1</assertj.version>
         <uberjar.name>benchmarks</uberjar.name>
-        <jmh.version>1.22</jmh.version>
         <eclipse.collections.version>10.0.0</eclipse.collections.version>
         <shade.plugin.version>3.2.4</shade.plugin.version>
     </properties>

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

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

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

@@ -2,7 +2,6 @@ package com.baeldung.genericarrays;
 
 import org.junit.Test;
 
-import java.util.ArrayList;
 import java.util.LinkedList;
 import java.util.List;
 

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

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

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

@@ -24,12 +24,12 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-core.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
 
         <dependency>
@@ -68,7 +68,6 @@
 
     <properties>
         <shade.plugin.version>3.2.0</shade.plugin.version>
-        <jmh.version>1.19</jmh.version>
         <assertj-core.version>3.10.0</assertj-core.version>
     </properties>
 </project>

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

@@ -31,12 +31,12 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-core.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
 
         <!-- Testing -->
@@ -77,7 +77,6 @@
     <properties>
         <shade.plugin.version>3.2.0</shade.plugin.version>
         <guava.version>28.2-jre</guava.version>
-        <jmh.version>1.19</jmh.version>
         <assertj-core.version>3.10.0</assertj-core.version>
     </properties>
 </project>

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

@@ -25,17 +25,16 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>${openjdk.jmh.version}</version>
+            <version>${jmh-core.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${openjdk.jmh.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
     </dependencies>
 
     <properties>
-        <openjdk.jmh.version>1.19</openjdk.jmh.version>
         <assertj.version>3.11.1</assertj.version>
     </properties>
 

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

@@ -24,7 +24,7 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>${openjdk.jmh.version}</version>
+            <version>${jmh-core.version}</version>
         </dependency>
         <dependency>
             <groupId>org.assertj</groupId>
@@ -40,7 +40,6 @@
     </dependencies>
 
     <properties>
-        <openjdk.jmh.version>1.19</openjdk.jmh.version>
         <assertj.version>3.11.1</assertj.version>
         <jol-core.version>0.10</jol-core.version>
     </properties>

core-java-modules/core-java-collections-4/README.md

@@ -5,3 +5,4 @@
 ### Relevant Articles: 
 
 - [ArrayList vs. LinkedList vs. HashMap in Java](https://www.baeldung.com/java-arraylist-vs-linkedlist-vs-hashmap)
+- [Java Deque vs. Stack](https://www.baeldung.com/java-deque-vs-stack)

core-java-modules/core-java-collections-list-3/pom.xml

@@ -58,7 +58,7 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh-core.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
     </dependencies>
 

core-java-modules/core-java-collections-list-3/src/main/java/com/baeldung/list/primitive/PrimitivesListPerformance.java

@@ -8,6 +8,7 @@ import org.openjdk.jmh.runner.options.Options;
 import org.openjdk.jmh.runner.options.OptionsBuilder;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
 
@@ -18,12 +19,12 @@ import java.util.concurrent.TimeUnit;
 @State(Scope.Thread)
 public class PrimitivesListPerformance {
 
-    private List<Integer> arrayList = new ArrayList<>();
+    private List<Integer> arrayList = new ArrayList<>(Arrays.asList(0, 1, 2, 3, 4, 5, 6, 7, 8, 9));
-    private TIntArrayList tList = new TIntArrayList();
+    private TIntArrayList tList = new TIntArrayList(new int[]{0, 1, 2, 3, 4, 5, 6, 7, 8, 9});
-    private cern.colt.list.IntArrayList coltList = new cern.colt.list.IntArrayList();
+    private cern.colt.list.IntArrayList coltList = new cern.colt.list.IntArrayList(new int[]{0, 1, 2, 3, 4, 5, 6, 7, 8, 9});
-    private IntArrayList fastUtilList = new IntArrayList();
+    private IntArrayList fastUtilList = new IntArrayList(new int[]{0, 1, 2, 3, 4, 5, 6, 7, 8, 9});
 
-    private int getValue = 10;
+    private int getValue = 4;
 
     @Benchmark
     public boolean addArrayList() {

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

@@ -8,4 +8,5 @@ This module contains articles about Map data structures in Java.
 - [The Map.computeIfAbsent() Method](https://www.baeldung.com/java-map-computeifabsent)
 - [Collections.synchronizedMap vs. ConcurrentHashMap](https://www.baeldung.com/java-synchronizedmap-vs-concurrenthashmap)
 - [Java HashMap Load Factor](https://www.baeldung.com/java-hashmap-load-factor)
+- [Converting java.util.Properties to HashMap](https://www.baeldung.com/java-convert-properties-to-hashmap)
 - More articles: [[<-- prev]](/core-java-modules/core-java-collections-maps-2)

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

@@ -25,17 +25,16 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>${openjdk.jmh.version}</version>
+            <version>${jmh-core.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${openjdk.jmh.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
     </dependencies>
 
     <properties>
-        <openjdk.jmh.version>1.19</openjdk.jmh.version>
         <assertj.version>3.11.1</assertj.version>
     </properties>
 

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

@@ -29,7 +29,7 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh-generator-annprocess.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
 
         <dependency>
@@ -51,8 +51,6 @@
     </build>
 
     <properties>
-        <jmh-core.version>1.19</jmh-core.version>
-        <jmh-generator-annprocess.version>1.19</jmh-generator-annprocess.version>
         <assertj.version>3.6.1</assertj.version>
     </properties>
 

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

@@ -23,12 +23,12 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-core.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
 		<dependency>
             <groupId>org.assertj</groupId>
@@ -39,7 +39,6 @@
     </dependencies>
 
     <properties>
-        <jmh.version>1.21</jmh.version>
         <guava.version>28.2-jre</guava.version>
          <!-- testing -->
         <assertj.version>3.6.1</assertj.version>

core-java-modules/core-java-concurrency-collections/src/test/java/com/baeldung/java/stream/ThreadPoolInParallelStreamIntegrationTest.java

@@ -21,14 +21,16 @@ public class ThreadPoolInParallelStreamIntegrationTest {
         long lastNum = 1_000_000;
 
         List<Long> aList = LongStream.rangeClosed(firstNum, lastNum).boxed().collect(Collectors.toList());
-
         ForkJoinPool customThreadPool = new ForkJoinPool(4);
-        long actualTotal = customThreadPool
-          .submit(() -> aList.parallelStream()
-            .reduce(0L, Long::sum))
-          .get();
 
+        try {
+            long actualTotal = customThreadPool
+              .submit(() -> aList.parallelStream().reduce(0L, Long::sum))
+              .get();
             assertEquals((lastNum + firstNum) * lastNum / 2, actualTotal);
+        } finally {
+            customThreadPool.shutdown();
+        }
     }
 
     @Test

core-java-modules/core-java-io-conversions/src/test/java/com/baeldung/filetoinputstream/JavaXToInputStreamUnitTest.java

@@ -5,12 +5,12 @@ import com.google.common.io.CharSource;
 import com.google.common.io.Files;
 import org.apache.commons.io.FileUtils;
 import org.apache.commons.io.IOUtils;
-import org.apache.commons.io.input.ReaderInputStream;
 import org.junit.Test;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.io.*;
+import java.nio.charset.StandardCharsets;
 
 public class JavaXToInputStreamUnitTest {
     protected final Logger logger = LoggerFactory.getLogger(getClass());
@@ -28,7 +28,7 @@ public class JavaXToInputStreamUnitTest {
     @Test
     public final void givenUsingGuava_whenConvertingStringToInputStream_thenCorrect() throws IOException {
         final String initialString = "text";
-        final InputStream targetStream = new ReaderInputStream(CharSource.wrap(initialString).openStream());
+        final InputStream targetStream = CharSource.wrap(initialString).asByteSource(StandardCharsets.UTF_8).openStream();
 
         IOUtils.closeQuietly(targetStream);
     }

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

@@ -77,7 +77,6 @@
         <assertj.version>3.6.1</assertj.version>
         <!-- instrumentation -->
         <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>

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

@@ -65,8 +65,6 @@
     </build>
 
     <properties>
-        <jmh-core.version>1.19</jmh-core.version>
-        <jmh-generator.version>1.19</jmh-generator.version>
         <assertj.version>3.12.2</assertj.version>
         <commons.beanutils.version>1.9.4</commons.beanutils.version>
         <guava.version>29.0-jre</guava.version>

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

@@ -0,0 +1,5 @@
+## Core Java Lang (Part 4)
+
+This module contains articles about core features in the Java language
+
+- [The Java final Keyword – Impact on Performance](https://www.baeldung.com/java-final-performance)

core-java-modules/core-java-lang-4/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-lang-4</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-lang-4</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>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${jmh-core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${jmh-generator.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-lang-4</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+      
+</project>

core-java-modules/core-java-lang-4/src/main/java/com/baeldung/finalkeyword/BenchmarkRunner.java

@@ -0,0 +1,34 @@
+package com.baeldung.finalkeyword;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+
+import java.util.concurrent.TimeUnit;
+
+public class BenchmarkRunner {
+
+    public static void main(String[] args) throws Exception {
+        org.openjdk.jmh.Main.main(args);
+    }
+
+    @Benchmark
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    @BenchmarkMode(Mode.AverageTime)
+    public static String concatNonFinalStrings() {
+        String x = "x";
+        String y = "y";
+        return x + y;
+    }
+
+    @Benchmark
+    @OutputTimeUnit(TimeUnit.NANOSECONDS)
+    @BenchmarkMode(Mode.AverageTime)
+    public static String concatFinalStrings() {
+        final String x = "x";
+        final String y = "y";
+        return x + y;
+    }
+
+}

core-java-modules/core-java-lang-4/src/main/java/com/baeldung/finalkeyword/ClassVariableFinal.java

@@ -0,0 +1,19 @@
+package com.baeldung.finalkeyword;
+
+import java.io.Console;
+
+public class ClassVariableFinal {
+
+    static final boolean doX = false;
+    static final boolean doY = true;
+
+    public static void main(String[] args) {
+        Console console = System.console();
+        if (doX) {
+            console.writer().println("x");
+        } else if (doY) {
+            console.writer().println("y");
+        }
+    }
+
+}

core-java-modules/core-java-lang-4/src/main/java/com/baeldung/finalkeyword/ClassVariableNonFinal.java

@@ -0,0 +1,19 @@
+package com.baeldung.finalkeyword;
+
+import java.io.Console;
+
+public class ClassVariableNonFinal {
+
+    static boolean doX = false;
+    static boolean doY = true;
+
+    public static void main(String[] args) {
+        Console console = System.console();
+        if (doX) {
+            console.writer().println("x");
+        } else if (doY) {
+            console.writer().println("y");
+        }
+    }
+
+}

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

@@ -58,7 +58,7 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
     </dependencies>
 
@@ -83,7 +83,6 @@
         <nd4j.version>1.0.0-beta4</nd4j.version>
         <colt.version>1.2.0</colt.version>
         <la4j.version>0.6.0</la4j.version>
-        <jmh.version>1.19</jmh.version>
     </properties>
 
 </project>

core-java-modules/core-java-lang-oop-types/src/main/java/com/baeldung/classfile/Outer.java

@@ -0,0 +1,135 @@
+package com.baeldung.classfile;
+
+import org.apache.commons.lang3.StringUtils;
+import com.baeldung.classfile.HelloWorld.HelloSomeone;
+
+public class Outer {
+
+    // Static Nested class
+    static class StaticNested {
+        public String message() {
+            return "This is a static Nested Class";
+        }
+    }
+
+    // Non-static Nested class
+    class Nested {
+        public String message() {
+            return "This is a non-static Nested Class";
+        }
+    }
+
+    // Local class
+    public String message() {
+        class Local {
+            private String message() {
+                return "This is a Local Class within a method";
+            }
+        }
+        Local local = new Local();
+        return local.message();
+    }
+
+    // Local class within if clause
+    public String message(String name) {
+        if (StringUtils.isEmpty(name)) {
+            class Local {
+                private String message() {
+                    return "This is a Local Class within if clause";
+                }
+            }
+            Local local = new Local();
+            return local.message();
+        } else
+            return "Welcome to " + name;
+    }
+
+    // Anonymous Inner class extending a class
+    public String greet() {
+        Outer anonymous = new Outer() {
+        	@Override
+            public String greet() {
+                return "Running Anonymous Class...";
+            }
+        };
+        return anonymous.greet();
+    }
+
+    // Anonymous inner class implementing an interface
+    public String greet(String name) {
+
+        HelloWorld helloWorld = new HelloWorld() {
+        	@Override
+            public String greet(String name) {
+                return "Welcome to " + name;
+            }
+
+        };
+        return helloWorld.greet(name);
+    }
+
+    // Anonymous inner class implementing nested interface
+    public String greetSomeone(String name) {
+    	
+        HelloSomeone helloSomeOne = new HelloSomeone() {
+        	@Override
+            public String greet(String name) {
+                return "Hello " + name;
+            }
+
+        };
+        return helloSomeOne.greet(name);
+    }
+
+    // Nested interface within a class
+    interface HelloOuter {
+        public String hello(String name);
+    }
+
+    // Enum within a class
+    enum Color {
+        RED, GREEN, BLUE;
+    }
+}
+
+interface HelloWorld {
+
+    public String greet(String name);
+
+    // Nested class within an interface
+    class InnerClass implements HelloWorld {
+    	@Override
+        public String greet(String name) {
+            return "Inner class within an interface";
+        }
+    }
+
+    // Nested interface within an interfaces
+    interface HelloSomeone {
+        public String greet(String name);
+    }
+
+    // Enum within an interface
+    enum Directon {
+        NORTH, SOUTH, EAST, WEST;
+    }
+}
+
+enum Level {
+    LOW, MEDIUM, HIGH;
+
+}
+
+enum Foods {
+
+    DRINKS, EATS;
+
+    // Enum within Enum
+    enum DRINKS {
+        APPLE_JUICE, COLA;
+    }
+
+    enum EATS {
+        POTATO, RICE;
+    }
+}

core-java-modules/core-java-lang-oop-types/src/test/java/com/baeldung/classfile/OuterUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.classfile;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import org.junit.jupiter.api.Test;
+import com.baeldung.classfile.Outer.Nested;
+
+public class OuterUnitTest {
+
+    @Test
+    public void when_static_nestedClass_then_verifyOutput() {
+        Outer.StaticNested nestedClass = new Outer.StaticNested();
+        assertEquals("This is a static Nested Class", nestedClass.message());
+    }
+
+    @Test
+    public void when_nestedClass_then_verifyOutput() {
+        Outer outer = new Outer();
+        Nested nestedClass = outer.new Nested();
+        assertEquals("This is a non-static Nested Class", nestedClass.message());
+    }
+
+    @Test
+    public void when_localClass_then_verifyOutput() {
+        Outer outer = new Outer();
+        assertEquals("This is a Local Class within a method", outer.message());
+    }
+
+    @Test
+    public void when_localClassInIfClause_then_verifyOutput() {
+        Outer outer = new Outer();
+        assertEquals("Welcome to Baeldung", outer.message("Baeldung"));
+        assertEquals("This is a Local Class within if clause", outer.message(""));
+    }
+
+    @Test
+    public void when_anonymousClass_then_verifyOutput() {
+        Outer outer = new Outer();
+        assertEquals("Running Anonymous Class...", outer.greet());
+    }
+
+    @Test
+    public void when_anonymousClassHelloWorld_then_verifyOutput() {
+        Outer outer = new Outer();
+        assertEquals("Welcome to Baeldung", outer.greet("Baeldung"));
+    }
+}

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

@@ -67,8 +67,6 @@
 
     <properties>
         <hibernate.core.version>5.4.0.Final</hibernate.core.version>
-        <jmh-core.version>1.19</jmh-core.version>
-        <jmh-generator.version>1.19</jmh-generator.version>
         <guava.version>27.1-jre</guava.version>
         <assertj.version>3.10.0</assertj.version>
         <rest-assured.version>3.1.1</rest-assured.version>

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

@@ -4,3 +4,4 @@
 - [Set Field Value With Reflection](https://www.baeldung.com/java-set-private-field-value)
 - [Checking If a Method is Static Using Reflection in Java](https://www.baeldung.com/java-check-method-is-static)
 - [Checking if a Java Class is ‘abstract’ Using Reflection](https://www.baeldung.com/java-reflection-is-class-abstract)
+- [Invoking a Private Method in Java](https://www.baeldung.com/java-call-private-method)

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

@@ -14,6 +14,15 @@
         <relativePath>../</relativePath>
     </parent>
     
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-test</artifactId>
+            <version>${spring.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+    
     <build>
         <finalName>core-java-reflection-2</finalName>
         <resources>
@@ -40,5 +49,6 @@
         <maven-compiler-plugin.version>3.8.0</maven-compiler-plugin.version>
         <source.version>1.8</source.version>
         <target.version>1.8</target.version>
+        <spring.version>5.3.4</spring.version>
     </properties>
 </project>

core-java-modules/core-java-reflection-2/src/main/java/com/baeldung/reflection/access/privatemethods/LongArrayUtil.java

@@ -0,0 +1,18 @@
+package com.baeldung.reflection.access.privatemethods;
+
+public class LongArrayUtil {
+
+    public static int indexOf(long[] array, long target) {
+        return indexOf(array, target, 0, array.length);
+    }
+
+    private static int indexOf(long[] array, long target, int start, int end) {
+        for (int i = start; i < end; i++) {
+            if (array[i] == target) {
+                return i;
+            }
+        }
+        return -1;
+    }
+
+}

core-java-modules/core-java-reflection-2/src/test/java/com/baeldung/reflection/access/privatemethods/InvokePrivateMethodsUnitTest.java

@@ -0,0 +1,28 @@
+package com.baeldung.reflection.access.privatemethods;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.test.util.ReflectionTestUtils;
+
+import java.lang.reflect.Method;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class InvokePrivateMethodsUnitTest {
+
+    private final long[] someLongArray = new long[] { 1L, 2L, 1L, 4L, 2L };
+
+    @Test
+    void whenSearchingForLongValueInSubsequenceUsingReflection_thenTheCorrectIndexOfTheValueIsReturned() throws Exception {
+        Method indexOfMethod = LongArrayUtil.class.getDeclaredMethod("indexOf", long[].class, long.class, int.class, int.class);
+        indexOfMethod.setAccessible(true);
+
+        assertEquals(2, indexOfMethod.invoke(LongArrayUtil.class, someLongArray, 1L, 1, someLongArray.length), "The index should be 2.");
+    }
+
+    @Test
+    void whenSearchingForLongValueInSubsequenceUsingSpring_thenTheCorrectIndexOfTheValueIsReturned() throws Exception {
+        int indexOfSearchTarget = ReflectionTestUtils.invokeMethod(LongArrayUtil.class, "indexOf", someLongArray, 1L, 1, someLongArray.length);
+        assertEquals(2, indexOfSearchTarget, "The index should be 2.");
+    }
+
+}

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

@@ -15,4 +15,5 @@ This module contains articles about core Java Security
 - [Security Context Basics: User, Subject and Principal](https://www.baeldung.com/security-context-basics)
 - [Java AES Encryption and Decryption](https://www.baeldung.com/java-aes-encryption-decryption)
 - [InvalidAlgorithmParameterException: Wrong IV Length](https://www.baeldung.com/java-invalidalgorithmparameter-exception)
+- [The java.security.egd JVM Option](https://www.baeldung.com/java-security-egd)
 - More articles: [[<-- prev]](/core-java-modules/core-java-security)

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

@@ -47,7 +47,6 @@
     </dependencies>
 
     <properties>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <maven.compiler.source>1.9</maven.compiler.source>
         <maven.compiler.target>1.9</maven.compiler.target>
         <assertj.version>3.11.1</assertj.version>

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

@@ -49,8 +49,6 @@
     <properties>
         <!-- testing -->
         <assertj.version>3.6.1</assertj.version>
-        <!-- plugins -->
-        <maven-surefire-plugin.version>2.22.1</maven-surefire-plugin.version>
     </properties>
 
 </project>

core-java-modules/core-java-streams-3/src/main/java/com/baeldung/streams/streamvscollection/StreamVsCollectionExample.java

@@ -0,0 +1,95 @@
+package com.baeldung.streams.streamvscollection;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.SortedSet;
+import java.util.TreeSet;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class StreamVsCollectionExample {
+
+    static ArrayList<String> userNameSource = new ArrayList<>();
+
+    static {
+        userNameSource.add("john");
+        userNameSource.add("smith");
+        userNameSource.add("tom");
+        userNameSource.add("rob");
+        userNameSource.add("charlie");
+        userNameSource.add("alfred"); 
+    }
+
+    public static Stream<String> userNames() {
+        return userNameSource.stream();
+    }
+
+    public static List<String> userNameList() {
+        return userNames().collect(Collectors.toList());
+    }
+
+    public static Set<String> userNameSet() {
+        return userNames().collect(Collectors.toSet());
+    }
+
+    public static Map<String, String> userNameMap() {
+        return userNames().collect(Collectors.toMap(u1 -> u1.toString(), u1 -> u1.toString()));
+    }
+
+    public static Stream<String> filterUserNames() {
+        return userNames().filter(i -> i.length() >= 4);
+    }
+
+    public static Stream<String> sortUserNames() {
+        return userNames().sorted();
+    }
+
+    public static Stream<String> limitUserNames() {
+        return userNames().limit(3);
+    }
+
+    public static Stream<String> sortFilterLimitUserNames() {
+        return filterUserNames().sorted().limit(3);
+    }
+
+    public static void printStream(Stream<String> stream) {
+        stream.forEach(System.out::println);
+    }
+
+    public static void modifyList() {
+        userNameSource.remove(2);
+    }
+
+    public static Map<String, String> modifyMap() {
+        Map<String, String> userNameMap = userNameMap();
+        userNameMap.put("bob", "bob");
+        userNameMap.remove("alfred");
+
+        return userNameMap;
+    }
+
+    public static void tryStreamTraversal() {
+        Stream<String> userNameStream = userNames();
+        userNameStream.forEach(System.out::println);
+        
+        try {
+            userNameStream.forEach(System.out::println);
+        } catch(IllegalStateException e) {
+            System.out.println("stream has already been operated upon or closed");
+        }
+    }
+    
+    public static void main(String[] args) {
+        System.out.println(userNameMap());
+        System.out.println(modifyMap());      
+        tryStreamTraversal();
+        
+        Set<String> set = userNames().collect(Collectors.toCollection(TreeSet::new));
+        set.forEach(val -> System.out.println(val));  
+        
+    }
+    
+    
+}

core-java-modules/core-java-string-algorithms-2/pom.xml

@@ -34,7 +34,7 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh-core.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
         <dependency>
             <groupId>org.assertj</groupId>

core-java-modules/core-java-string-algorithms/pom.xml

@@ -39,7 +39,7 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${jmh-core.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
         <dependency>
             <groupId>com.vdurmont</groupId>

core-java-modules/multimodulemavenproject/pom.xml

@@ -59,7 +59,6 @@
         <compiler.plugin.version>3.8.0</compiler.plugin.version>
         <source.version>1.9</source.version>
         <target.version>1.9</target.version>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <assertj-core.version>3.12.2</assertj-core.version>
     </properties>
 

core-java-modules/pom.xml

@@ -82,6 +82,7 @@
         <module>core-java-lang</module>
         <module>core-java-lang-2</module>
         <module>core-java-lang-3</module>
+        <module>core-java-lang-4</module>
         <module>core-java-lang-math</module>
         <module>core-java-lang-math-2</module>
         <module>core-java-lang-math-3</module>
@@ -147,18 +148,6 @@
         </dependencies>
     </dependencyManagement>
 
-    <build>
-        <pluginManagement>
-            <plugins>
-                <plugin>
-                    <groupId>org.apache.maven.plugins</groupId>
-                    <artifactId>maven-surefire-plugin</artifactId>
-                    <version>${maven-surefire-plugin.version}</version>
-                </plugin>
-            </plugins>
-        </pluginManagement>
-    </build>
-
     <properties>
         <maven-surefire-plugin.version>2.22.2</maven-surefire-plugin.version>
         <junit-jupiter.version>5.6.2</junit-jupiter.version>

custom-pmd/pom.xml

@@ -45,7 +45,6 @@
     </build>
 
     <properties>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <maven-compiler-plugin.version>3.7.0</maven-compiler-plugin.version>
         <pmdVersion>6.0.1</pmdVersion>
         <maven.compiler.source>1.8</maven.compiler.source>

data-structures/src/main/java/com/baeldung/circularbuffer/CircularBuffer.java

@@ -10,10 +10,8 @@ public class CircularBuffer<E> {
 
     @SuppressWarnings("unchecked")
     public CircularBuffer(int capacity) {
-
         this.capacity = (capacity < 1) ? DEFAULT_CAPACITY : capacity;
-        this.data = (E[]) new Object[capacity];
+        this.data = (E[]) new Object[this.capacity];
-
         this.readSequence = 0;
         this.writeSequence = -1;
     }

data-structures/src/main/java/com/baeldung/circularlinkedlist/CircularLinkedList.java

@@ -5,7 +5,7 @@ import org.slf4j.LoggerFactory;
 
 public class CircularLinkedList {
 
-    final Logger LOGGER = LoggerFactory.getLogger(CircularLinkedList.class);
+    final Logger logger = LoggerFactory.getLogger(CircularLinkedList.class);
 
     private Node head = null;
     private Node tail = null;
@@ -42,25 +42,30 @@ public class CircularLinkedList {
     }
 
     public void deleteNode(int valueToDelete) {
-
         Node currentNode = head;
-
+        if (head == null) {
-        if (head != null) {
+            return;
-            if (currentNode.value == valueToDelete) {
+        }
-                head = head.nextNode;
-                tail.nextNode = head;
-            } else {
         do {
             Node nextNode = currentNode.nextNode;
             if (nextNode.value == valueToDelete) {
+                if (tail == head) {
+                    head = null;
+                    tail = null;
+                } else {
                     currentNode.nextNode = nextNode.nextNode;
+                    if (head == nextNode) {
+                        head = head.nextNode;
+                    }
+                    if (tail == nextNode) {
+                        tail = currentNode;
+                    }
+                }
                 break;
             }
-                    currentNode = currentNode.nextNode;
+            currentNode = nextNode;
         } while (currentNode != head);
     }
-        }
-    }
 
     public void traverseList() {
 
@@ -68,7 +73,7 @@ public class CircularLinkedList {
 
         if (head != null) {
             do {
-                LOGGER.info(currentNode.value + " ");
+                logger.info(currentNode.value + " ");
                 currentNode = currentNode.nextNode;
             } while (currentNode != head);
         }

data-structures/src/main/java/com/baeldung/tree/BinaryTree.java

@@ -148,48 +148,46 @@ public class BinaryTree {
         }
     }
 
-    
     public void traverseInOrderWithoutRecursion() {
-        Stack<Node> stack = new Stack<Node>();
+        Stack<Node> stack = new Stack<>();
         Node current = root;
-        stack.push(root);
+
-        while(! stack.isEmpty()) {
+        while (current != null || !stack.isEmpty()) {
-            while(current.left != null) {
+            while (current != null) {
+                stack.push(current);
                 current = current.left;
-                stack.push(current);                
-            }
-            current = stack.pop();
-            visit(current.value);
-            if(current.right != null) {
-                current = current.right;                
-                stack.push(current);
             }
+
+            Node top = stack.pop();
+            visit(top.value);
+            current = top.right;
         }
     }
 
     public void traversePreOrderWithoutRecursion() {
-        Stack<Node> stack = new Stack<Node>();
+        Stack<Node> stack = new Stack<>();
         Node current = root;
         stack.push(root);
-        while(! stack.isEmpty()) {
+
+        while (current != null && !stack.isEmpty()) {
             current = stack.pop();
             visit(current.value);
 
-            if(current.right != null)
+            if (current.right != null)
                 stack.push(current.right);
 
-            if(current.left != null)
+            if (current.left != null)
                 stack.push(current.left);
         }
     }
     
     public void traversePostOrderWithoutRecursion() {
-        Stack<Node> stack = new Stack<Node>();
+        Stack<Node> stack = new Stack<>();
         Node prev = root;
         Node current = root;
         stack.push(root);
 
-        while (!stack.isEmpty()) {
+        while (current != null && !stack.isEmpty()) {
             current = stack.peek();
             boolean hasChild = (current.left != null || current.right != null);
             boolean isPrevLastChild = (prev == current.right || (prev == current.left && current.right == null));

data-structures/src/test/java/com/baeldung/circularlinkedlist/CircularLinkedListUnitTest.java

@@ -1,10 +1,10 @@
 package com.baeldung.circularlinkedlist;
 
+import org.junit.Test;
+
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
-import org.junit.Test;
-
 public class CircularLinkedListUnitTest {
 
     @Test
@@ -23,7 +23,7 @@ public class CircularLinkedListUnitTest {
     }
 
     @Test
-    public void givenACircularLinkedList_WhenDeletingElements_ThenListDoesNotContainThoseElements() {
+    public void givenACircularLinkedList_WhenDeletingInOrderHeadMiddleTail_ThenListDoesNotContainThoseElements() {
         CircularLinkedList cll = createCircularLinkedList();
 
         assertTrue(cll.containsNode(13));
@@ -39,6 +39,32 @@ public class CircularLinkedListUnitTest {
         assertFalse(cll.containsNode(46));
     }
 
+    @Test
+    public void givenACircularLinkedList_WhenDeletingInOrderTailMiddleHead_ThenListDoesNotContainThoseElements() {
+        CircularLinkedList cll = createCircularLinkedList();
+
+        assertTrue(cll.containsNode(46));
+        cll.deleteNode(46);
+        assertFalse(cll.containsNode(46));
+
+        assertTrue(cll.containsNode(1));
+        cll.deleteNode(1);
+        assertFalse(cll.containsNode(1));
+
+        assertTrue(cll.containsNode(13));
+        cll.deleteNode(13);
+        assertFalse(cll.containsNode(13));
+    }
+
+    @Test
+    public void givenACircularLinkedListWithOneNode_WhenDeletingElement_ThenListDoesNotContainTheElement() {
+        CircularLinkedList cll = new CircularLinkedList();
+        cll.addNode(1);
+        cll.deleteNode(1);
+        assertFalse(cll.containsNode(1));
+    }
+
+
     private CircularLinkedList createCircularLinkedList() {
         CircularLinkedList cll = new CircularLinkedList();
 

data-structures/src/test/java/com/baeldung/tree/BinaryTreeUnitTest.java

@@ -13,7 +13,7 @@ public class BinaryTreeUnitTest {
 
         BinaryTree bt = createBinaryTree();
 
-        assertTrue(!bt.isEmpty());
+        assertFalse(bt.isEmpty());
     }
 
     @Test
@@ -72,6 +72,7 @@ public class BinaryTreeUnitTest {
 
     @Test
     public void it_deletes_the_root() {
+
         int value = 12;
         BinaryTree bt = new BinaryTree();
         bt.add(value);
@@ -91,6 +92,14 @@ public class BinaryTreeUnitTest {
         bt.traverseInOrderWithoutRecursion();
     }
 
+    @Test
+    public void givenAnEmptyBinaryTree_WhenTraversingInOrderWithoutRecursion_ThenNoException() {
+
+        BinaryTree empty = new BinaryTree();
+
+        empty.traverseInOrderWithoutRecursion();
+    }
+
     @Test
     public void givenABinaryTree_WhenTraversingPreOrder_ThenPrintValues() {
 
@@ -101,6 +110,14 @@ public class BinaryTreeUnitTest {
         bt.traversePreOrderWithoutRecursion();
     }
 
+    @Test
+    public void givenAnEmptyBinaryTree_WhenTraversingPreOrderWithoutRecursion_ThenNoException() {
+
+        BinaryTree empty = new BinaryTree();
+
+        empty.traversePreOrderWithoutRecursion();
+    }
+
     @Test
     public void givenABinaryTree_WhenTraversingPostOrder_ThenPrintValues() {
 
@@ -111,6 +128,14 @@ public class BinaryTreeUnitTest {
         bt.traversePostOrderWithoutRecursion();
     }
 
+    @Test
+    public void givenAnEmptyBinaryTree_WhenTraversingPostOrderWithoutRecursion_ThenNoException() {
+
+        BinaryTree empty = new BinaryTree();
+
+        empty.traversePostOrderWithoutRecursion();
+    }
+
     @Test
     public void givenABinaryTree_WhenTraversingLevelOrder_ThenPrintValues() {
 

ddd-modules/mainapp/pom.xml

@@ -29,7 +29,6 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-surefire-plugin</artifactId>
-                <version>2.16</version>
                 <configuration>
                     <enableAssertions>true</enableAssertions>
                 </configuration>

ddd-modules/pom.xml

@@ -66,7 +66,6 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-surefire-plugin</artifactId>
-                <version>${maven-surefire-plugin.version}</version>
                 <configuration>
                     <forkCount>0</forkCount>
                 </configuration>
@@ -75,13 +74,10 @@
     </build>
 
     <properties>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-
         <source.version>9</source.version>
         <target.version>9</target.version>
 
         <compiler.plugin.version>3.8.1</compiler.plugin.version>
-        <maven-surefire-plugin.version>2.22.2</maven-surefire-plugin.version>
 
         <appmodules.version>1.0</appmodules.version>
 

ddd/pom.xml

@@ -99,15 +99,6 @@
         </dependency>
     </dependencies>
 
-    <build>
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-surefire-plugin</artifactId>
-            </plugin>
-        </plugins>
-    </build>
-
     <properties>
         <joda-money.version>1.0.1</joda-money.version>
 

google-web-toolkit/pom.xml

@@ -97,7 +97,6 @@
             <!-- Skip normal test execution, we use gwt:test instead -->
             <plugin>
                 <artifactId>maven-surefire-plugin</artifactId>
-                <version>${surefire.plugin.version}</version>
                 <configuration>
                     <skip>true</skip>
                 </configuration>
@@ -113,12 +112,8 @@
         <maven.compiler.source>1.8</maven.compiler.source>
         <maven.compiler.target>1.8</maven.compiler.target>
 
-        <!-- Don't let your Mac use a crazy non-standard encoding -->
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <gwt.version>2.8.2</gwt.version>
         <gwt.plugin.version>1.0-rc-8</gwt.plugin.version>
-        <surefire.plugin.version>2.17</surefire.plugin.version>
     </properties>
 
 </project>

guava-modules/guava-collections-list/pom.xml

@@ -66,14 +66,6 @@
                 <filtering>true</filtering>
             </resource>
         </resources>
-
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-surefire-plugin</artifactId>
-                <version>2.22.2</version>
-            </plugin>
-        </plugins>
     </build>
 
     <properties>

guava-modules/guava-collections-map/pom.xml

@@ -38,14 +38,6 @@
                 <filtering>true</filtering>
             </resource>
         </resources>
-
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-surefire-plugin</artifactId>
-                <version>2.22.2</version>
-            </plugin>
-        </plugins>
     </build>
 
     <properties>

guava-modules/guava-collections-set/pom.xml

@@ -37,14 +37,6 @@
 
     <build>
         <finalName>guava-collections-set</finalName>
-
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-surefire-plugin</artifactId>
-                <version>2.22.2</version>
-            </plugin>
-        </plugins>
     </build>
 
     <properties>

guava-modules/guava-collections/pom.xml

@@ -71,14 +71,6 @@
                 <filtering>true</filtering>
             </resource>
         </resources>
-
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-surefire-plugin</artifactId>
-                <version>2.22.2</version>
-            </plugin>
-        </plugins>
     </build>
 
     <properties>

guava-modules/guava-io/pom.xml

@@ -40,14 +40,6 @@
                 <filtering>true</filtering>
             </resource>
         </resources>
-
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-surefire-plugin</artifactId>
-                <version>2.22.2</version>
-            </plugin>
-        </plugins>
     </build>
 
 </project>

guava-modules/guava-utilities/pom.xml

@@ -52,14 +52,6 @@
                 <filtering>true</filtering>
             </resource>
         </resources>
-
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-surefire-plugin</artifactId>
-                <version>2.22.2</version>
-            </plugin>
-        </plugins>
     </build>
 
     <properties>

guava-modules/pom.xml

@@ -46,17 +46,8 @@
         </dependency>
     </dependencies>
 
-    <build>
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-surefire-plugin</artifactId>
-                <version>2.22.2</version>
-            </plugin>
-        </plugins>
-    </build>
-
     <properties>
+        <maven-surefire-plugin.version>2.22.2</maven-surefire-plugin.version>
         <junit-jupiter.version>5.6.2</junit-jupiter.version>
         <guava.version>29.0-jre</guava.version>
     </properties>

jackson-modules/pom.xml

@@ -50,16 +50,6 @@
         </dependency>
     </dependencies>
 
-    <build>
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-surefire-plugin</artifactId>
-                <version>2.22.2</version>
-            </plugin>
-        </plugins>
-    </build>
-
     <properties>
         <junit-jupiter.version>5.6.2</junit-jupiter.version>
     </properties>

jackson-simple/pom.xml

@@ -51,14 +51,6 @@
                 <filtering>true</filtering>
             </resource>
         </resources>
-
-        <plugins>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-surefire-plugin</artifactId>
-                <version>2.22.2</version>
-            </plugin>
-        </plugins>
     </build>
 
     <properties>

java-collections-maps-3/README.md

@@ -3,3 +3,4 @@
 - [Java Map With Case-Insensitive Keys](https://www.baeldung.com/java-map-with-case-insensitive-keys)
 - [Using a Byte Array as Map Key in Java](https://www.baeldung.com/java-map-key-byte-array)
 - [Using the Map.Entry Java Class](https://www.baeldung.com/java-map-entry)
+- [Optimizing HashMap’s Performance](https://www.baeldung.com/java-hashmap-optimize-performance)

java-rmi/src/test/java/com/baeldung/rmi/JavaRMIIntegrationTest.java

@@ -1,32 +1,32 @@
 package com.baeldung.rmi;
 
-import static org.junit.Assert.assertEquals;
+import org.junit.Before;
-import static org.junit.Assert.fail;
+import org.junit.Test;
 
 import java.rmi.NotBoundException;
 import java.rmi.RemoteException;
 import java.rmi.registry.LocateRegistry;
 import java.rmi.registry.Registry;
 
-import org.junit.BeforeClass;
+import static org.junit.Assert.assertEquals;
-import org.junit.Test;
+import static org.junit.Assert.fail;
 
 public class JavaRMIIntegrationTest {
 
-	@BeforeClass
+    private MessengerServiceImpl messengerService;
-	public static void whenRunServer_thenServerStarts() {
 
+    @Before
+    public void init() {
         try {
-			MessengerServiceImpl server = new MessengerServiceImpl();
+            messengerService = new MessengerServiceImpl();
-			server.createStubAndBind();
+            messengerService.createStubAndBind();
         } catch (RemoteException e) {
-			fail("Exception Occurred");
+            fail("Exception Occurred: " + e);
         }
     }
 
     @Test
     public void whenClientSendsMessageToServer_thenServerSendsResponseMessage() {
-		
         try {
             Registry registry = LocateRegistry.getRegistry();
             MessengerService server = (MessengerService) registry.lookup("MessengerService");
@@ -34,10 +34,8 @@ public class JavaRMIIntegrationTest {
 
             String expectedMessage = "Server Message";
             assertEquals(responseMessage, expectedMessage);
-		} catch (RemoteException e) {
+        } catch (RemoteException | NotBoundException e) {
-			fail("Exception Occurred");
+            fail("Exception Occurred: " + e);
-		} catch (NotBoundException nb) {
-			fail("Exception Occurred");
         }
     }
 

jee-7/pom.xml

@@ -523,7 +523,6 @@
         <jersey.version>2.25</jersey.version>
         <arquillian-glassfish.version>1.0.0.Final</arquillian-glassfish.version>
         <org.springframework.security.version>4.2.3.RELEASE</org.springframework.security.version>
-        <maven-surefire-plugin.version>2.21.0</maven-surefire-plugin.version>
         <taglibs.standard.version>1.1.2</taglibs.standard.version>
         <com.sun.faces.jsf.version>2.2.14</com.sun.faces.jsf.version>
         <httpclient.version>4.5</httpclient.version>

jee-7/src/test/java/com/baeldung/batch/understanding/CustomCheckPointIntegrationTest.java

@@ -12,7 +12,7 @@ import javax.batch.runtime.StepExecution;
 
 import org.junit.jupiter.api.Test;
 
-class CustomCheckPointUnitTest {
+class CustomCheckPointIntegrationTest {
     @Test
     public void givenChunk_whenCustomCheckPoint_thenCommitCountIsThree() throws Exception {
         JobOperator jobOperator = BatchRuntime.getJobOperator();

jee-7/src/test/java/com/baeldung/batch/understanding/JobSequenceIntegrationTest.java

@@ -16,7 +16,7 @@ import javax.batch.runtime.StepExecution;
 
 import org.junit.jupiter.api.Test;
 
-class JobSequenceUnitTest {
+class JobSequenceIntegrationTest {
     @Test
     public void givenTwoSteps_thenBatch_CompleteWithSuccess() throws Exception {
         JobOperator jobOperator = BatchRuntime.getJobOperator();

jee-7/src/test/java/com/baeldung/batch/understanding/SimpleBatchLetIntegrationTest.java

@@ -11,7 +11,7 @@ import javax.batch.runtime.JobExecution;
 
 import org.junit.jupiter.api.Test;
 
-class SimpleBatchLetUnitTest {
+class SimpleBatchLetIntegrationTest {
     @Test
     public void givenBatchLet_thenBatch_CompleteWithSuccess() throws Exception {
         JobOperator jobOperator = BatchRuntime.getJobOperator();

jee-7/src/test/java/com/baeldung/batch/understanding/SimpleChunkIntegrationTest.java

@@ -16,7 +16,7 @@ import javax.batch.runtime.StepExecution;
 
 import org.junit.jupiter.api.Test;
 
-class SimpleChunkUnitTest {
+class SimpleChunkIntegrationTest {
     @Test
     public void givenChunk_thenBatch_CompletesWithSucess() throws Exception {
         JobOperator jobOperator = BatchRuntime.getJobOperator();

jee-7/src/test/java/com/baeldung/batch/understanding/SimpleErrorChunkIntegrationTest.java

@@ -13,7 +13,7 @@ import javax.batch.runtime.StepExecution;
 
 import org.junit.jupiter.api.Test;
 
-class SimpleErrorChunkUnitTest {
+class SimpleErrorChunkIntegrationTest {
 
     @Test
     public void givenChunkError_thenBatch_CompletesWithFailed() throws Exception {

jhipster-5/bookstore-monolith/pom.xml

@@ -1099,8 +1099,6 @@
         <scala.version>2.12.6</scala.version>
         <node.version>v10.15.0</node.version>
         <npm.version>6.4.1</npm.version>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <project.testresult.directory>${project.build.directory}/test-results</project.testresult.directory>
         <maven.build.timestamp.format>yyyyMMddHHmmss</maven.build.timestamp.format>
         <maven.compiler.source>${java.version}</maven.compiler.source>

jhipster/jhipster-uaa/gateway/pom.xml

@@ -1020,8 +1020,6 @@
         <scala.version>2.12.6</scala.version>
         <node.version>v8.12.0</node.version>
         <npm.version>6.4.1</npm.version>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <project.testresult.directory>${project.build.directory}/test-results</project.testresult.directory>
         <maven.build.timestamp.format>yyyyMMddHHmmss</maven.build.timestamp.format>
         <maven.compiler.source>${java.version}</maven.compiler.source>

jhipster/jhipster-uaa/quotes/pom.xml

@@ -840,8 +840,6 @@
         <scala.version>2.12.6</scala.version>
         <node.version>v8.12.0</node.version>
         <npm.version>6.4.1</npm.version>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <project.testresult.directory>${project.build.directory}/test-results</project.testresult.directory>
         <maven.build.timestamp.format>yyyyMMddHHmmss</maven.build.timestamp.format>
         <maven.compiler.source>${java.version}</maven.compiler.source>

jhipster/jhipster-uaa/uaa/pom.xml

@@ -842,8 +842,6 @@
         <scala.version>2.12.6</scala.version>
         <node.version>v8.12.0</node.version>
         <npm.version>6.4.1</npm.version>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <project.testresult.directory>${project.build.directory}/test-results</project.testresult.directory>
         <maven.build.timestamp.format>yyyyMMddHHmmss</maven.build.timestamp.format>
         <maven.compiler.source>${java.version}</maven.compiler.source>

jjwt/README.md

@@ -47,3 +47,4 @@ Available commands (assumes httpie - https://github.com/jkbrzt/httpie):
 ## Relevant articles:
 
 - [Supercharge Java Authentication with JSON Web Tokens (JWTs)](https://www.baeldung.com/java-json-web-tokens-jjwt)
+- [Decode a JWT Token in Java](https://www.baeldung.com/java-jwt-token-decode)

jjwt/pom.xml

@@ -41,6 +41,12 @@
             <artifactId>jjwt</artifactId>
             <version>${jjwt.version}</version>
         </dependency>
+
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <properties>

jjwt/src/main/java/io/jsonwebtoken/jjwtfun/util/JWTDecoderUtil.java

@@ -0,0 +1,46 @@
+package io.jsonwebtoken.jjwtfun.util;
+
+import io.jsonwebtoken.SignatureAlgorithm;
+import io.jsonwebtoken.impl.crypto.DefaultJwtSignatureValidator;
+
+import javax.crypto.spec.SecretKeySpec;
+import java.util.Base64;
+
+import static io.jsonwebtoken.SignatureAlgorithm.HS256;
+
+public class JWTDecoderUtil {
+
+    public static String decodeJWTToken(String token) {
+        Base64.Decoder decoder = Base64.getDecoder();
+
+        String[] chunks = token.split("\\.");
+
+        String header = new String(decoder.decode(chunks[0]));
+        String payload = new String(decoder.decode(chunks[1]));
+
+        return header + " " + payload;
+    }
+
+    public static String decodeJWTToken(String token, String secretKey) throws Exception {
+        Base64.Decoder decoder = Base64.getDecoder();
+
+        String[] chunks = token.split("\\.");
+
+        String header = new String(decoder.decode(chunks[0]));
+        String payload = new String(decoder.decode(chunks[1]));
+
+        String tokenWithoutSignature = chunks[0] + "." + chunks[1];
+        String signature = chunks[2];
+
+        SignatureAlgorithm sa = HS256;
+        SecretKeySpec secretKeySpec = new SecretKeySpec(secretKey.getBytes(), sa.getJcaName());
+
+        DefaultJwtSignatureValidator validator = new DefaultJwtSignatureValidator(sa, secretKeySpec);
+
+        if (!validator.isValid(tokenWithoutSignature, signature)) {
+            throw new Exception("Could not verify JWT token integrity!");
+        }
+
+        return header + " " + payload;
+    }
+}

jjwt/src/test/java/io/jsonwebtoken/jjwtfun/util/JWTDecoderUtilUnitTest.java

@@ -0,0 +1,32 @@
+package io.jsonwebtoken.jjwtfun.util;
+
+import io.jsonwebtoken.SignatureAlgorithm;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class JWTDecoderUtilUnitTest {
+
+    private final static String SIMPLE_TOKEN = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkJhZWxkdW5nIFVzZXIiLCJpYXQiOjE1MTYyMzkwMjJ9";
+    private final static String SIGNED_TOKEN = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkJhZWxkdW5nIFVzZXIiLCJpYXQiOjE1MTYyMzkwMjJ9.qH7Zj_m3kY69kxhaQXTa-ivIpytKXXjZc1ZSmapZnGE";
+
+    @Test
+    void givenSimpleToken_whenDecoding_thenStringOfHeaderPayloadAreReturned() {
+        assertThat(JWTDecoderUtil.decodeJWTToken(SIMPLE_TOKEN))
+          .contains(SignatureAlgorithm.HS256.getValue());
+    }
+
+    @Test
+    void givenSignedToken_whenDecodingWithInvalidSecret_thenIntegrityIsNotValidated() {
+        assertThatThrownBy(() -> JWTDecoderUtil.decodeJWTToken(SIGNED_TOKEN, "BAD_SECRET"))
+          .hasMessage("Could not verify JWT token integrity!");
+    }
+
+    @Test
+    void givenSignedToken_whenDecodingWithValidSecret_thenIntegrityIsValidated() throws Exception {
+        assertThat(JWTDecoderUtil.decodeJWTToken(SIGNED_TOKEN, "MySecretKey"))
+          .contains("Baeldung User");
+    }
+}

jmeter/README.md

@@ -52,3 +52,4 @@ Enjoy it :)
 
 - [Intro to Performance Testing using JMeter](https://www.baeldung.com/jmeter)
 - [Configure Jenkins to Run and Show JMeter Tests](https://www.baeldung.com/jenkins-and-jmeter)
+- [Write Extracted Data to a File Using JMeter](https://www.baeldung.com/jmeter-write-to-file)

jmh/pom.xml

@@ -19,12 +19,12 @@
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-core</artifactId>
-            <version>${openjdk.jmh.version}</version>
+            <version>${jmh-core.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jmh</groupId>
             <artifactId>jmh-generator-annprocess</artifactId>
-            <version>${openjdk.jmh.version}</version>
+            <version>${jmh-generator.version}</version>
         </dependency>
         <dependency>
             <groupId>org.openjdk.jol</groupId>
@@ -76,7 +76,6 @@
     </build>
 
     <properties>
-        <openjdk.jmh.version>1.19</openjdk.jmh.version>
         <maven-jar-plugin.version>3.0.2</maven-jar-plugin.version>
         <jol-core.version>0.10</jol-core.version>
         <maven-assembly-plugin.version>3.2.0</maven-assembly-plugin.version>

kubernetes/k8s-intro/README.md

@@ -0,0 +1,17 @@
+# Kubernetes Java API Sample Code
+
+This module contains sample code used to show how to use the Kubernetes client Java API.
+
+Before running those samples, make sure that your environment is correctly configured to access
+a working Kubernetes cluster.
+
+An easy way to check that everything is working as expected is issuing any *kubectl get* command:
+
+```shell
+$ kubectl get nodes
+```
+If you get a valid response, then you're good to go.
+
+### Relevant Articles:
+
+- [Paging and Async Calls with the Kubernetes API](https://www.baeldung.com/java-kubernetes-paging-async)

kubernetes/k8s-intro/pom.xml

@@ -0,0 +1,41 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>kubernetes-parent</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+    <artifactId>k8s-intro</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+
+    <dependencies>
+        <dependency>
+            <groupId>io.kubernetes</groupId>
+            <artifactId>client-java</artifactId>
+            <version>11.0.0</version>
+        </dependency>
+
+        <dependency>
+            <groupId>ch.qos.logback</groupId>
+            <artifactId>logback-classic</artifactId>
+            <version>1.2.3</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.8.1</version>
+                <configuration>
+                    <!-- http://maven.apache.org/plugins/maven-compiler-plugin/ -->
+                    <source>1.8</source>
+                    <target>1.8</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+</project>

kubernetes/k8s-intro/src/main/java/com/baeldung/kubernetes/intro/ApiInvoker.java

@@ -0,0 +1,11 @@
+package com.baeldung.kubernetes.intro;
+
+import io.kubernetes.client.openapi.ApiCallback;
+import io.kubernetes.client.openapi.ApiException;
+import io.kubernetes.client.openapi.apis.CoreV1Api;
+import okhttp3.Call;
+
+@FunctionalInterface
+public interface ApiInvoker<R> {
+    Call apply(CoreV1Api api, ApiCallback<R> callback) throws ApiException;
+}

kubernetes/k8s-intro/src/main/java/com/baeldung/kubernetes/intro/AsyncHelper.java

@@ -0,0 +1,74 @@
+package com.baeldung.kubernetes.intro;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Future;
+import java.util.function.BiFunction;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import io.kubernetes.client.openapi.ApiCallback;
+import io.kubernetes.client.openapi.ApiException;
+import io.kubernetes.client.openapi.apis.CoreV1Api;
+import okhttp3.Call;
+
+public class AsyncHelper<R>  implements ApiCallback<R> {
+    
+    private static final Logger log = LoggerFactory.getLogger(AsyncHelper.class);
+    
+    private CoreV1Api api;
+    private CompletableFuture<R> callResult;
+    
+    private AsyncHelper(CoreV1Api api) {
+        this.api = api;
+    }
+    
+    public static <T> CompletableFuture<T> doAsync(CoreV1Api api, ApiInvoker<T> invoker) {
+        
+        AsyncHelper<T> p = new AsyncHelper<>(api);
+        return p.execute(invoker);
+    }
+    
+    private CompletableFuture<R> execute( ApiInvoker<R> invoker) {
+        
+        try {
+            callResult = new CompletableFuture<>();
+            log.info("[I38] Calling API...");
+            final Call call = invoker.apply(api,this);
+            log.info("[I41] API Succesfully invoked: method={}, url={}",
+              call.request().method(),
+              call.request().url());
+            return callResult;
+        }
+        catch(ApiException aex) {
+            callResult.completeExceptionally(aex);
+            return callResult;
+        }
+    }
+
+    @Override
+    public void onFailure(ApiException e, int statusCode, Map<String, List<String>> responseHeaders) {
+        log.error("[E53] onFailure",e);
+        callResult.completeExceptionally(e);
+    }
+
+    @Override
+    public void onSuccess(R result, int statusCode, Map<String, List<String>> responseHeaders) {
+        log.error("[E61] onSuccess: statusCode={}",statusCode);
+        callResult.complete(result);
+    }
+
+    @Override
+    public void onUploadProgress(long bytesWritten, long contentLength, boolean done) {
+        log.info("[E61] onUploadProgress: bytesWritten={}, contentLength={}, done={}",bytesWritten,contentLength,done);
+    }
+
+    @Override
+    public void onDownloadProgress(long bytesRead, long contentLength, boolean done) {
+        log.info("[E75] onDownloadProgress: bytesRead={}, contentLength={}, done={}",bytesRead,contentLength,done);
+    }
+}
+

kubernetes/k8s-intro/src/main/java/com/baeldung/kubernetes/intro/ListNodes.java

@@ -0,0 +1,31 @@
+/**
+ * 
+ */
+package com.baeldung.kubernetes.intro;
+
+
+import io.kubernetes.client.openapi.ApiClient;
+import io.kubernetes.client.openapi.apis.CoreV1Api;
+import io.kubernetes.client.openapi.models.V1NodeList;
+import io.kubernetes.client.util.Config;
+
+/**
+ * @author Philippe
+ *
+ */
+public class ListNodes {
+
+    /**
+     * @param args
+     */
+    public static void main(String[] args) throws Exception {
+        
+        ApiClient client  = Config.defaultClient();
+        CoreV1Api api = new CoreV1Api(client);
+        V1NodeList nodeList = api.listNode(null, null, null, null, null, null, null, null, 10, false);
+        nodeList.getItems()
+          .stream()
+          .forEach((node) -> System.out.println(node.getMetadata()));
+    }
+
+}

kubernetes/k8s-intro/src/main/java/com/baeldung/kubernetes/intro/ListNodesAsync.java

@@ -0,0 +1,50 @@
+/**
+ * 
+ */
+package com.baeldung.kubernetes.intro;
+
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.TimeUnit;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import io.kubernetes.client.openapi.ApiClient;
+import io.kubernetes.client.openapi.apis.CoreV1Api;
+import io.kubernetes.client.openapi.models.V1NodeList;
+import io.kubernetes.client.util.Config;
+
+/**
+ * @author Philippe
+ *
+ */
+public class ListNodesAsync {
+    
+    private static Logger log = LoggerFactory.getLogger(ListNodesAsync.class);
+    /**
+     * @param args
+     */
+    public static void main(String[] args) throws Exception {
+        
+        // Initial setup
+        ApiClient client  = Config.defaultClient();
+        CoreV1Api api = new CoreV1Api(client);
+        
+        // Start async call
+        CompletableFuture<V1NodeList> p = AsyncHelper.doAsync(api,(capi,cb) ->
+          capi.listNodeAsync(null, null, null, null, null, null, null, null, 10, false, cb)
+        );
+        
+        p.thenAcceptAsync((nodeList) -> {
+            log.info("[I40] Processing results...");
+            nodeList.getItems()
+            .stream()
+            .forEach((node) -> System.out.println(node.getMetadata()));
+        });
+        
+        log.info("[I46] Waiting results...");
+        p.get(10, TimeUnit.SECONDS);
+    }
+
+}

kubernetes/k8s-intro/src/main/java/com/baeldung/kubernetes/intro/ListPodsPaged.java

@@ -0,0 +1,46 @@
+/**
+ * 
+ */
+package com.baeldung.kubernetes.intro;
+
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import io.kubernetes.client.openapi.ApiClient;
+import io.kubernetes.client.openapi.apis.CoreV1Api;
+import io.kubernetes.client.openapi.models.V1NodeList;
+import io.kubernetes.client.openapi.models.V1PodList;
+import io.kubernetes.client.util.Config;
+
+/**
+ * @author Philippe
+ *
+ */
+public class ListPodsPaged {
+    
+    private static final Logger log = LoggerFactory.getLogger(ListPodsPaged.class);
+
+    /**
+     * @param args
+     */
+    public static void main(String[] args) throws Exception {
+        
+        ApiClient client  = Config.defaultClient();
+        CoreV1Api api = new CoreV1Api(client);
+        String continuationToken = null;
+        int limit = 2; // Just for illustration purposes. Real world values would range from ~100 to ~1000/page 
+        Long remaining = null; 
+        do {
+            log.info("==========================================================================");
+            log.info("Retrieving data: continuationToken={}, remaining={}", continuationToken,remaining);
+            V1PodList items = api.listPodForAllNamespaces(null, continuationToken, null, null, limit, null, null, null, 10, false);
+            continuationToken = items.getMetadata().getContinue();
+            remaining = items.getMetadata().getRemainingItemCount();
+            items.getItems()
+              .stream()
+              .forEach((node) -> System.out.println(node.getMetadata()));
+        } while( continuationToken != null );
+    }
+
+}

kubernetes/k8s-intro/src/test/java/com/baeldung/kubernetes/intro/ListNodesAsyncLiveTest.java

@@ -0,0 +1,10 @@
+package com.baeldung.kubernetes.intro;
+
+import org.junit.jupiter.api.Test;
+
+class ListNodesAsyncLiveTest {
+    @Test
+    void whenListNodes_thenSuccess()  throws Exception {
+        ListNodesAsync.main(new String[] {});
+    }
+}

kubernetes/k8s-intro/src/test/java/com/baeldung/kubernetes/intro/ListNodesLiveTest.java

@@ -0,0 +1,10 @@
+package com.baeldung.kubernetes.intro;
+
+import org.junit.jupiter.api.Test;
+
+class ListNodesLiveTest {
+    @Test
+    void whenListNodes_thenSuccess()  throws Exception {
+        ListNodes.main(new String[] {});
+    }
+}

kubernetes/k8s-intro/src/test/java/com/baeldung/kubernetes/intro/ListPodsPagedLiveTest.java

@@ -0,0 +1,10 @@
+package com.baeldung.kubernetes.intro;
+
+import org.junit.jupiter.api.Test;
+
+class ListPodsPagedLiveTest {
+    @Test
+    void whenListPodsPage_thenSuccess()  throws Exception {
+        ListPodsPaged.main(new String[] {});
+    }
+}

kubernetes/k8s-intro/src/test/resources/logback.xml

@@ -0,0 +1,11 @@
+<configuration>
+  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+    <encoder>
+      <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
+    </encoder>
+  </appender>
+
+  <root level="debug">
+    <appender-ref ref="STDOUT" />
+  </root>
+</configuration>