[BAEL-10866] - Resolved conflicts

core-java-11/README.md

@@ -0,0 +1,5 @@
+### Relevant articles
+
+- [Java 11 Single File Source Code](https://www.baeldung.com/java-single-file-source-code)
+- [Java 11 Local Variable Syntax for Lambda Parameters](https://www.baeldung.com/java-var-lambda-params)
+

core-java-11/src/test/java/com/baeldung/NewStringAPIUnitTest.java

@@ -0,0 +1,43 @@
+package com.baeldung;
+
+import static org.hamcrest.CoreMatchers.is;
+
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class NewStringAPIUnitTest {
+
+    @Test
+    public void whenRepeatStringTwice_thenGetStringTwice() {
+        String output = "La ".repeat(2) + "Land";
+
+        is(output).equals("La La Land");
+    }
+
+    @Test
+    public void whenStripString_thenReturnStringWithoutWhitespaces() {
+        is("\n\t  hello   \u2005".strip()).equals("hello");
+    }
+
+    @Test
+    public void whenTrimAdvanceString_thenReturnStringWithWhitespaces() {
+        is("\n\t  hello   \u2005".trim()).equals("hello   \u2005");
+    }
+
+    @Test
+    public void whenBlankString_thenReturnTrue() {
+        assertTrue("\n\t\u2005  ".isBlank());
+    }
+
+    @Test
+    public void whenMultilineString_thenReturnNonEmptyLineCount() {
+        String multilineStr = "This is\n \n a multiline\n string.";
+
+        long lineCount = multilineStr.lines()
+          .filter(String::isBlank)
+          .count();
+
+        is(lineCount).equals(3L);
+    }
+}

core-java-8/README.md

@@ -15,7 +15,6 @@
 - [Guide to Java 8 Comparator.comparing()](http://www.baeldung.com/java-8-comparator-comparing)
 - [Guide To Java 8 Optional](http://www.baeldung.com/java-optional)
 - [Guide to the Java 8 forEach](http://www.baeldung.com/foreach-java)
-- [Java Base64 Encoding and Decoding](http://www.baeldung.com/java-base64-encode-and-decode)
 - [The Difference Between map() and flatMap()](http://www.baeldung.com/java-difference-map-and-flatmap)
 - [Static and Default Methods in Interfaces in Java](http://www.baeldung.com/java-static-default-methods)
 - [Efficient Word Frequency Calculator in Java](http://www.baeldung.com/java-word-frequency)

core-java-8/src/test/java/com/baeldung/java8/Java8PredicateChainUnitTest.java

@@ -0,0 +1,131 @@
+package com.baeldung.java8;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.contains;
+import static org.junit.Assert.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+import org.junit.Test;
+
+public class Java8PredicateChainUnitTest {
+    
+    private List<String> names = Arrays.asList("Adam", "Alexander", "John", "Tom");
+
+    @Test
+    public void whenFilterList_thenSuccess() {
+        List<String> result = names.stream()
+            .filter(name -> name.startsWith("A"))
+            .collect(Collectors.toList());
+
+        assertEquals(2, result.size());
+        assertThat(result, contains("Adam", "Alexander"));
+    }
+
+    @Test
+    public void whenFilterListWithMultipleFilters_thenSuccess() {
+        List<String> result = names.stream()
+            .filter(name -> name.startsWith("A"))
+            .filter(name -> name.length() < 5)
+            .collect(Collectors.toList());
+        
+        assertEquals(1, result.size());
+        assertThat(result, contains("Adam"));
+    }
+
+    @Test
+    public void whenFilterListWithComplexPredicate_thenSuccess() {
+        List<String> result = names.stream()
+            .filter(name -> name.startsWith("A") && name.length() < 5)
+            .collect(Collectors.toList());
+        
+        assertEquals(1, result.size());
+        assertThat(result, contains("Adam"));
+    }
+
+    @Test
+    public void whenFilterListWithCombinedPredicatesInline_thenSuccess() {
+        List<String> result = names.stream()
+            .filter(((Predicate<String>) name -> name.startsWith("A")).and(name -> name.length() < 5))
+            .collect(Collectors.toList());
+        
+        assertEquals(1, result.size());
+        assertThat(result, contains("Adam"));
+    }
+
+    @Test
+    public void whenFilterListWithCombinedPredicatesUsingAnd_thenSuccess() {
+        Predicate<String> predicate1 = str -> str.startsWith("A");
+        Predicate<String> predicate2 = str -> str.length() < 5;
+
+        List<String> result = names.stream()
+            .filter(predicate1.and(predicate2))
+            .collect(Collectors.toList());
+
+        assertEquals(1, result.size());
+        assertThat(result, contains("Adam"));
+    }
+
+    @Test
+    public void whenFilterListWithCombinedPredicatesUsingOr_thenSuccess() {
+        Predicate<String> predicate1 = str -> str.startsWith("J");
+        Predicate<String> predicate2 = str -> str.length() < 4;
+
+        List<String> result = names.stream()
+            .filter(predicate1.or(predicate2))
+            .collect(Collectors.toList());
+
+        assertEquals(2, result.size());
+        assertThat(result, contains("John", "Tom"));
+    }
+
+    @Test
+    public void whenFilterListWithCombinedPredicatesUsingOrAndNegate_thenSuccess() {
+        Predicate<String> predicate1 = str -> str.startsWith("J");
+        Predicate<String> predicate2 = str -> str.length() < 4;
+
+        List<String> result = names.stream()
+            .filter(predicate1.or(predicate2.negate()))
+            .collect(Collectors.toList());
+
+        assertEquals(3, result.size());
+        assertThat(result, contains("Adam", "Alexander", "John"));
+    }
+
+    @Test
+    public void whenFilterListWithCollectionOfPredicatesUsingAnd_thenSuccess() {
+        List<Predicate<String>> allPredicates = new ArrayList<Predicate<String>>();
+        allPredicates.add(str -> str.startsWith("A"));
+        allPredicates.add(str -> str.contains("d"));
+        allPredicates.add(str -> str.length() > 4);
+
+        List<String> result = names.stream()
+            .filter(allPredicates.stream()
+                .reduce(x -> true, Predicate::and))
+            .collect(Collectors.toList());
+
+        assertEquals(1, result.size());
+        assertThat(result, contains("Alexander"));
+    }
+
+    @Test
+    public void whenFilterListWithCollectionOfPredicatesUsingOr_thenSuccess() {
+        List<Predicate<String>> allPredicates = new ArrayList<Predicate<String>>();
+        allPredicates.add(str -> str.startsWith("A"));
+        allPredicates.add(str -> str.contains("d"));
+        allPredicates.add(str -> str.length() > 4);
+
+        List<String> result = names.stream()
+            .filter(allPredicates.stream()
+                .reduce(x -> false, Predicate::or))
+            .collect(Collectors.toList());
+
+        assertEquals(2, result.size());
+        assertThat(result, contains("Adam", "Alexander"));
+    }
+
+}

core-java-9/README.md

@@ -9,7 +9,6 @@
 - [Java 9 Convenience Factory Methods for Collections](http://www.baeldung.com/java-9-collections-factory-methods) 
 - [New Stream Collectors in Java 9](http://www.baeldung.com/java9-stream-collectors)
 - [Java 9 CompletableFuture API Improvements](http://www.baeldung.com/java-9-completablefuture)
-- [Spring Security – Redirect to the Previous URL After Login](http://www.baeldung.com/spring-security-redirect-login)
 - [Java 9 Process API Improvements](http://www.baeldung.com/java-9-process-api)
 - [Introduction to Java 9 StackWalking API](http://www.baeldung.com/java-9-stackwalking-api)
 - [Introduction to Project Jigsaw](http://www.baeldung.com/project-jigsaw-java-modularity)

core-java-arrays/src/main/java/com/baeldung/arraycopy/model/Employee.java

@@ -7,6 +7,14 @@ public class Employee implements Serializable {
     private int id;
     private String name;
 
+    public Employee() {
+    }
+
+    public Employee(int id, String name) {
+        this.id = id;
+        this.name = name;
+    }
+
     public int getId() {
         return id;
     }

core-java-arrays/src/test/java/com/baeldung/sort/ArraySortUnitTest.java

@@ -0,0 +1,90 @@
+package com.baeldung.sort;
+
+import com.baeldung.arraycopy.model.Employee;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.stream.IntStream;
+
+import static org.junit.Assert.assertArrayEquals;
+
+public class ArraySortUnitTest {
+    private Employee[] employees;
+    private int[] numbers;
+    private String[] strings;
+
+    private Employee john = new Employee(6, "John");
+    private Employee mary = new Employee(3, "Mary");
+    private Employee david = new Employee(4, "David");
+
+    @Before
+    public void setup() {
+        createEmployeesArray();
+        createNumbersArray();
+        createStringArray();
+    }
+
+    private void createEmployeesArray() {
+        employees = new Employee[]{john, mary, david};
+    }
+
+    private void createNumbersArray() {
+        numbers = new int[]{-8, 7, 5, 9, 10, -2, 3};
+    }
+
+    private void createStringArray() {
+        strings = new String[]{"learning", "java", "with", "baeldung"};
+    }
+
+    @Test
+    public void givenIntArray_whenSortingAscending_thenCorrectlySorted() {
+        Arrays.sort(numbers);
+
+        assertArrayEquals(new int[]{-8, -2, 3, 5, 7, 9, 10}, numbers);
+    }
+
+    @Test
+    public void givenIntArray_whenSortingDescending_thenCorrectlySorted() {
+        numbers = IntStream.of(numbers).boxed().sorted(Comparator.reverseOrder()).mapToInt(i -> i).toArray();
+
+        assertArrayEquals(new int[]{10, 9, 7, 5, 3, -2, -8}, numbers);
+    }
+
+    @Test
+    public void givenStringArray_whenSortingAscending_thenCorrectlySorted() {
+        Arrays.sort(strings);
+
+        assertArrayEquals(new String[]{"baeldung", "java", "learning", "with"}, strings);
+    }
+
+    @Test
+    public void givenStringArray_whenSortingDescending_thenCorrectlySorted() {
+        Arrays.sort(strings, Comparator.reverseOrder());
+
+        assertArrayEquals(new String[]{"with", "learning", "java", "baeldung"}, strings);
+    }
+
+    @Test
+    public void givenObjectArray_whenSortingAscending_thenCorrectlySorted() {
+        Arrays.sort(employees, Comparator.comparing(Employee::getName));
+
+        assertArrayEquals(new Employee[]{david, john, mary}, employees);
+    }
+
+    @Test
+    public void givenObjectArray_whenSortingDescending_thenCorrectlySorted() {
+        Arrays.sort(employees, Comparator.comparing(Employee::getName).reversed());
+
+        assertArrayEquals(new Employee[]{mary, john, david}, employees);
+    }
+
+    @Test
+    public void givenObjectArray_whenSortingMultipleAttributesAscending_thenCorrectlySorted() {
+        Arrays.sort(employees, Comparator.comparing(Employee::getName).thenComparing(Employee::getId));
+
+        assertArrayEquals(new Employee[]{david, john, mary}, employees);
+    }
+
+}

core-java-collections/src/test/java/org/baeldung/java/lists/ListJUnitTest.java

@@ -5,6 +5,10 @@ import org.junit.Test;
 
 import java.util.Arrays;
 import java.util.List;
+import java.util.Set;
+import java.util.HashSet;
+
+import java.util.stream.Collectors;
 
 public class ListJUnitTest {
 
@@ -18,4 +22,26 @@ public class ListJUnitTest {
         Assert.assertNotSame(list1, list2);
         Assert.assertNotEquals(list1, list3);
     }
+
+    @Test
+    public void whenIntersection_ShouldReturnCommonElements() throws Exception {
+        List<String> list = Arrays.asList("red", "blue", "blue", "green", "red");
+        List<String> otherList = Arrays.asList("red", "green", "green", "yellow");
+
+        Set<String> commonElements = new HashSet(Arrays.asList("red", "green"));
+
+        Set<String> result = list.stream()
+          .distinct()
+          .filter(otherList::contains)
+          .collect(Collectors.toSet());
+
+        Assert.assertEquals(commonElements, result);
+
+        Set<String> inverseResult = otherList.stream()
+          .distinct()
+          .filter(list::contains)
+          .collect(Collectors.toSet());
+
+        Assert.assertEquals(commonElements, inverseResult);
+    }
 }

core-java-lang/src/main/java/com/baeldung/controlstructures/ConditionalBranches.java

@@ -0,0 +1,68 @@
+package com.baeldung.controlstructures;
+
+public class ConditionalBranches {
+
+    /**
+     * Multiple if/else/else if statements examples. Shows different syntax usage.
+     */
+    public static void ifElseStatementsExamples() {
+        int count = 2; // Initial count value.
+
+        // Basic syntax. Only one statement follows. No brace usage.
+        if (count > 1)
+            System.out.println("Count is higher than 1");
+
+        // Basic syntax. More than one statement can be included. Braces are used (recommended syntax).
+        if (count > 1) {
+            System.out.println("Count is higher than 1");
+            System.out.println("Count is equal to: " + count);
+        }
+
+        // If/Else syntax. Two different courses of action can be included.
+        if (count > 2) {
+            System.out.println("Count is higher than 2");
+        } else {
+            System.out.println("Count is lower or equal than 2");
+        }
+
+        // If/Else/Else If syntax. Three or more courses of action can be included.
+        if (count > 2) {
+            System.out.println("Count is higher than 2");
+        } else if (count <= 0) {
+            System.out.println("Count is less or equal than zero");
+        } else {
+            System.out.println("Count is either equal to one, or two");
+        }
+    }
+
+    /**
+     * Ternary Operator example.
+     * @see ConditionalBranches#ifElseStatementsExamples()
+     */
+    public static void ternaryExample() {
+        int count = 2;
+        System.out.println(count > 2 ? "Count is higher than 2" : "Count is lower or equal than 2");
+    }
+
+    /**
+     * Switch structure example. Shows how to replace multiple if/else statements with one structure.
+     */
+    public static void switchExample() {
+        int count = 3;
+        switch (count) {
+        case 0:
+            System.out.println("Count is equal to 0");
+            break;
+        case 1:
+            System.out.println("Count is equal to 1");
+            break;
+        case 2:
+            System.out.println("Count is equal to 2");
+            break;
+        default:
+            System.out.println("Count is either negative, or higher than 2");
+            break;
+        }
+    }
+
+}

core-java-lang/src/main/java/com/baeldung/controlstructures/Loops.java

@@ -0,0 +1,123 @@
+package com.baeldung.controlstructures;
+
+public class Loops {
+
+    /**
+     * Dummy method. Only prints a generic message.
+     */
+    private static void methodToRepeat() {
+        System.out.println("Dummy method.");
+    }
+
+    /**
+     * Shows how to iterate 50 times with 3 different method/control structures.
+     */
+    public static void repetitionTo50Examples() {
+        for (int i = 1; i <= 50; i++) {
+            methodToRepeat();
+        }
+
+        int whileCounter = 1;
+        while (whileCounter <= 50) {
+            methodToRepeat();
+            whileCounter++;
+        }
+
+        int count = 1;
+        do {
+            methodToRepeat();
+            count++;
+        } while (count < 50);
+    }
+
+    /**
+     * Splits a sentence in words, and prints each word in a new line.
+     * @param sentence Sentence to print as independent words.
+     */
+    public static void printWordByWord(String sentence) {
+        for (String word : sentence.split(" ")) {
+            System.out.println(word);
+        }
+    }
+
+    /**
+     * Prints text an N amount of times. Shows usage of the {@code break} branching statement.
+     * @param textToPrint Text to repeatedly print.
+     * @param times Amount to times to print received text.
+     */
+    public static void printTextNTimes(String textToPrint, int times) {
+        int counter = 1;
+        while (true) {
+            System.out.println(textToPrint);
+            if (counter == times) {
+                break;
+            }
+        }
+    }
+
+    /**
+     * Prints text an N amount of times, up to 50. Shows usage of the {@code break} branching statement.
+     * @param textToPrint Text to repeatedly print.
+     * @param times Amount to times to print received text. If times is higher than 50, textToPrint will only be printed 50 times.
+     */
+    public static void printTextNTimesUpTo50(String textToPrint, int times) {
+        int counter = 1;
+        while (counter < 50) {
+            System.out.println(textToPrint);
+            if (counter == times) {
+                break;
+            }
+        }
+    }
+
+    /**
+     * Prints an specified amount of even numbers. Shows usage of both {@code break} and {@code continue} branching statements.
+     * @param amountToPrint Amount of even numbers to print.
+     */
+    public static void printEvenNumbers(int amountToPrint) {
+        if (amountToPrint <= 0) { // Invalid input
+            return;
+        }
+        int iterator = 0;
+        int amountPrinted = 0;
+        while (true) {
+            if (iterator % 2 == 0) { // Is an even number
+                System.out.println(iterator);
+                amountPrinted++;
+                iterator++;
+            } else {
+                iterator++;
+                continue; // Won't print
+            }
+            if (amountPrinted == amountToPrint) {
+                break;
+            }
+        }
+    }
+
+    /**
+     * Prints an specified amount of even numbers, up to 100. Shows usage of both {@code break} and {@code continue} branching statements.
+     * @param amountToPrint Amount of even numbers to print.
+     */
+    public static void printEvenNumbersToAMaxOf100(int amountToPrint) {
+        if (amountToPrint <= 0) { // Invalid input
+            return;
+        }
+        int iterator = 0;
+        int amountPrinted = 0;
+        while (amountPrinted < 100) {
+            if (iterator % 2 == 0) { // Is an even number
+                System.out.println(iterator);
+                amountPrinted++;
+                iterator++;
+            } else {
+                iterator++;
+                continue; // Won't print
+            }
+            if (amountPrinted == amountToPrint) {
+                break;
+            }
+        }
+    }
+
+}

core-java-sun/src/main/java/com/baeldung/README.md

@@ -1,2 +1 @@
 ### Relevant Articles:
-- [SHA-256 Hashing in Java](http://www.baeldung.com/sha-256-hashing-java)

core-java/README.md

@@ -14,25 +14,20 @@
 - [Pattern Search with Grep in Java](http://www.baeldung.com/grep-in-java)
 - [URL Encoding and Decoding in Java](http://www.baeldung.com/java-url-encoding-decoding)
 - [How to Create an Executable JAR with Maven](http://www.baeldung.com/executable-jar-with-maven)
-- [How to Design a Genetic Algorithm in Java](http://www.baeldung.com/java-genetic-algorithm)
 - [Basic Introduction to JMX](http://www.baeldung.com/java-management-extensions)
-- [AWS Lambda With Java](http://www.baeldung.com/java-aws-lambda)
 - [Introduction to Nashorn](http://www.baeldung.com/java-nashorn)
 - [Java Money and the Currency API](http://www.baeldung.com/java-money-and-currency)
 - [JVM Log Forging](http://www.baeldung.com/jvm-log-forging)
 - [Guide to sun.misc.Unsafe](http://www.baeldung.com/java-unsafe)
 - [How to Perform a Simple HTTP Request in Java](http://www.baeldung.com/java-http-request)
 - [How to Add a Single Element to a Stream](http://www.baeldung.com/java-stream-append-prepend)
-- [Kotlin Java Interoperability](http://www.baeldung.com/kotlin-java-interoperability)
 - [How to Find all Getters Returning Null](http://www.baeldung.com/java-getters-returning-null)
 - [How to Get a Name of a Method Being Executed?](http://www.baeldung.com/java-name-of-executing-method)
-- [Converting a Stack Trace to a String in Java](http://www.baeldung.com/java-stacktrace-to-string)
 - [Introduction to Java Serialization](http://www.baeldung.com/java-serialization)
 - [Guide to UUID in Java](http://www.baeldung.com/java-uuid)
 - [Guide to Escaping Characters in Java RegExps](http://www.baeldung.com/java-regexp-escape-char)
 - [Difference between URL and URI](http://www.baeldung.com/java-url-vs-uri)
 - [Broadcasting and Multicasting in Java](http://www.baeldung.com/java-broadcast-multicast)
-- [Period and Duration in Java](http://www.baeldung.com/java-period-duration)
 - [OutOfMemoryError: GC Overhead Limit Exceeded](http://www.baeldung.com/java-gc-overhead-limit-exceeded)
 - [Creating a Java Compiler Plugin](http://www.baeldung.com/java-build-compiler-plugin)
 - [Quick Guide to Java Stack](http://www.baeldung.com/java-stack)
@@ -41,9 +36,8 @@
 - [A Guide to ThreadLocalRandom in Java](http://www.baeldung.com/java-thread-local-random)
 - [Compiling Java *.class Files with javac](http://www.baeldung.com/javac)
 - [A Guide to Iterator in Java](http://www.baeldung.com/java-iterator)
-- [The Trie Data Structure in Java](http://www.baeldung.com/trie-java)
 - [Introduction to Javadoc](http://www.baeldung.com/javadoc)
-- [Guide to Externalizable Interface in Java](http://www.baeldung.com/java-externalizable)
+- [Guide to the Externalizable Interface in Java](http://www.baeldung.com/java-externalizable)
 - [A Practical Guide to DecimalFormat](http://www.baeldung.com/java-decimalformat)
 - [How to Detect the OS Using Java](http://www.baeldung.com/java-detect-os)
 - [ASCII Art in Java](http://www.baeldung.com/ascii-art-in-java)
@@ -84,7 +78,6 @@
 - [Understanding Memory Leaks in Java](https://www.baeldung.com/java-memory-leaks)
 - [A Guide to SimpleDateFormat](https://www.baeldung.com/java-simple-date-format)
 - [SSL Handshake Failures](https://www.baeldung.com/java-ssl-handshake-failures)
-- [Implementing a Binary Tree in Java](https://www.baeldung.com/java-binary-tree)
 - [Changing the Order in a Sum Operation Can Produce Different Results?](https://www.baeldung.com/java-floating-point-sum-order)
 - [Java – Try with Resources](https://www.baeldung.com/java-try-with-resources)
 - [Abstract Classes in Java](https://www.baeldung.com/java-abstract-class)

core-java/src/main/java/com/baeldung/README.md

@@ -1,2 +1 @@
 ### Relevant Articles:
-- [SHA-256 Hashing in Java](http://www.baeldung.com/sha-256-hashing-java)

core-java/src/main/java/com/baeldung/gc/VerboseGarbageCollectorRunner.java

@@ -0,0 +1,63 @@
+package com.baeldung.gc;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * A simple Java program to demonstrate how to enable verbose Garbage Collection (GC) logging.
+ * <p>
+ * This simple program loads 3 million {@link java.lang.String} instances into a {@link java.util.HashMap} 
+ * object before making an explicit call to the garbage collector using <code>System.gc()</code>.
+ * <p>
+ * Finally, it removes 2 million of the {@link java.lang.String} instances from the {@link java.util.HashMap}. 
+ * We also explicitly use <code>System.out.println</code> to make interpreting the output easier.
+ * <p>
+ * Run this program with the following arguments to see verbose GC logging in its complete form:
+ * <pre>
+ * -XX:+UseSerialGC -Xms1024m -Xmx1024m -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintGCDateStamps -Xloggc:/path/to/file/gc.log
+ * </pre>
+ * Where:
+ * <ul>
+ *   <li><code>-XX:+UseSerialGC</code> - specify the serial garbage collector.</li>
+ *   <li><code>-Xms1024m</code> - specify the minimal heap size.</li>
+ *   <li><code>-Xmx1024m</code> - specify the maximal heap size.</li>
+ *   <li><code>-verbose:gc</code> - activate the logging of garbage collection information in its simplest form.</li>
+ *   <li><code>-XX:+PrintGCDetails</code> - activate detailed information about garbage collection.</li>
+ *   <li><code>-XX:+PrintGCTimeStamps</code> - include a timestamp in the output reflecting the real-time passed in seconds since the JVM started.</li>
+ *   <li><code>-XX:+PrintGCDateStamps</code> - include the absolute date and time at the start of each line.</li>
+ *   <li><code>-Xloggc</code> - by default the GC log is written to stdout. Specify an output file via this argument.</li>
+ * </ul>
+ * <p>
+ * It should be noted that the first three arguments are not strictly necessary but for the purposes or the example
+ * help really simplify things.
+ *
+ */
+public class VerboseGarbageCollectorRunner {
+
+    private static Map<String, String> stringContainer = new HashMap<>();
+
+    public static void main(String[] args) {
+        System.out.println("Start of program!");
+        String stringWithPrefix = "stringWithPrefix";
+
+        // Load Java Heap with 3 M java.lang.String instances
+        for (int i = 0; i < 3000000; i++) {
+            String newString = stringWithPrefix + i;
+            stringContainer.put(newString, newString);
+        }
+        System.out.println("MAP size: " + stringContainer.size());
+
+        // Explicit GC!
+        System.gc();
+
+        // Remove 2 M out of 3 M
+        for (int i = 0; i < 2000000; i++) {
+            String newString = stringWithPrefix + i;
+            stringContainer.remove(newString);
+        }
+
+        System.out.println("MAP size: " + stringContainer.size());
+        System.out.println("End of program!");
+    }
+
+}

core-java/src/main/java/com/baeldung/nativekeyword/DateTimeUtils.java

@@ -0,0 +1,10 @@
+package com.baeldung.nativekeyword;
+
+public class DateTimeUtils {
+
+    public native String getSystemTime();
+
+    static {
+        System.loadLibrary("nativedatetimeutils");
+    }
+}

core-java/src/main/java/com/baeldung/nativekeyword/NativeMainApp.java

@@ -0,0 +1,11 @@
+package com.baeldung.nativekeyword;
+
+import com.baeldung.nativekeyword.DateTimeUtils;
+
+public class NativeMainApp {
+    public static void main(String[] args) {
+        DateTimeUtils dateTimeUtils = new DateTimeUtils();
+        String input = dateTimeUtils.getSystemTime();
+        System.out.println("System time is : " + input);
+    }
+}

core-java/src/test/java/com/baeldung/nativekeyword/DateTimeUtilsManualTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.nativekeyword;
+
+import static org.junit.Assert.assertNotNull;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.slf4j.Logger;
+
+public class DateTimeUtilsManualTest {
+
+    private static final Logger LOG = org.slf4j.LoggerFactory.getLogger(DateTimeUtilsManualTest.class);
+
+    @BeforeClass
+    public static void setUpClass() {
+        System.loadLibrary("msvcr100");
+        System.loadLibrary("libgcc_s_sjlj-1");
+        System.loadLibrary("libstdc++-6");
+        System.loadLibrary("nativedatetimeutils");
+    }
+
+    @Test
+    public void givenNativeLibsLoaded_thenNativeMethodIsAccessible() {
+        DateTimeUtils dateTimeUtils = new DateTimeUtils();
+        LOG.info("System time is : " + dateTimeUtils.getSystemTime());
+        assertNotNull(dateTimeUtils.getSystemTime());
+    }
+}

core-kotlin/README.md

@@ -34,7 +34,6 @@
 - [Kotlin Constructors](https://www.baeldung.com/kotlin-constructors)
 - [Creational Design Patterns in Kotlin: Builder](https://www.baeldung.com/kotlin-builder-pattern)
 - [Kotlin Nested and Inner Classes](https://www.baeldung.com/kotlin-inner-classes)
-- [Kotlin with Ktor](https://www.baeldung.com/kotlin-ktor)
 - [Fuel HTTP Library with Kotlin](https://www.baeldung.com/kotlin-fuel)
 - [Introduction to Kovenant Library for Kotlin](https://www.baeldung.com/kotlin-kovenant)
 - [Converting Kotlin Data Class from JSON using GSON](https://www.baeldung.com/kotlin-json-convert-data-class)

core-kotlin/src/main/kotlin/com/baeldung/contract/CallsInPlaceEffect.kt

@@ -0,0 +1,23 @@
+package com.baeldung.contract
+
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
+
+@ExperimentalContracts
+inline fun <R> myRun(block: () -> R): R {
+    contract {
+        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
+    }
+    return block()
+}
+
+@ExperimentalContracts
+fun callsInPlace() {
+    val i: Int
+    myRun {
+        i = 1 // Without contract initialization is forbidden due to possible re-assignment
+    }
+    println(i) // Without contract variable might be uninitialized
+}
+

core-kotlin/src/main/kotlin/com/baeldung/contract/ReturnsEffect.kt

@@ -0,0 +1,43 @@
+package com.baeldung.contract
+
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
+
+data class Request(val arg: String)
+
+class Service {
+
+    @ExperimentalContracts
+    fun process(request: Request?) {
+        validate(request)
+        println(request.arg)
+    }
+
+}
+
+@ExperimentalContracts
+private fun validate(request: Request?) {
+    contract {
+        returns() implies (request != null)
+    }
+    if (request == null) {
+        throw IllegalArgumentException("Undefined request")
+    }
+}
+
+data class MyEvent(val message: String)
+
+@ExperimentalContracts
+fun processEvent(event: Any?) {
+    if (isInterested(event)) {
+        println(event.message) // Compiler makes smart cast here with the help of contract
+    }
+}
+
+@ExperimentalContracts
+fun isInterested(event: Any?): Boolean {
+    contract {
+        returns(true) implies (event is MyEvent)
+    }
+    return event is MyEvent
+}

core-kotlin/src/test/kotlin/com/baeldung/kotlin/constant/ConstantUnitTest.kt

@@ -0,0 +1,17 @@
+import com.baeldung.kotlin.constant.TestKotlinConstantClass
+import com.baeldung.kotlin.constant.TestKotlinConstantObject
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+class ConstantUnitTest {
+
+    @Test
+    fun givenConstant_whenCompareWithActualValue_thenReturnTrue() {
+        assertEquals(10, TestKotlinConstantObject.COMPILE_TIME_CONST)
+        assertEquals(30, TestKotlinConstantObject.RUN_TIME_CONST)
+        assertEquals(20, TestKotlinConstantObject.JAVA_STATIC_FINAL_FIELD)
+
+        assertEquals(40, TestKotlinConstantClass.COMPANION_OBJECT_NUMBER)
+    }
+}
+

core-kotlin/src/test/kotlin/com/baeldung/kotlin/constant/TestKotlinConstantClass.kt

@@ -0,0 +1,8 @@
+package com.baeldung.kotlin.constant
+
+
+class TestKotlinConstantClass {
+    companion object {
+        const val COMPANION_OBJECT_NUMBER = 40
+    }
+}

core-kotlin/src/test/kotlin/com/baeldung/kotlin/constant/TestKotlinConstantObject.kt

@@ -0,0 +1,15 @@
+package com.baeldung.kotlin.constant
+
+
+object TestKotlinConstantObject {
+    const val COMPILE_TIME_CONST = 10
+
+    val RUN_TIME_CONST: Int
+
+    @JvmField
+    val JAVA_STATIC_FINAL_FIELD = 20
+
+    init {
+        RUN_TIME_CONST = TestKotlinConstantObject.COMPILE_TIME_CONST + 20;
+    }
+}

data-structures/README.md

@@ -1,4 +1,4 @@
 ## Relevant articles:
 
-- [The Trie Data Structure in Java](http://www.baeldung.com/trie-java)
-- [Implementing a Binary Tree in Java](http://www.baeldung.com/java-binary-tree)
+[The Trie Data Structure in Java](https://www.baeldung.com/trie-java)
+[Implementing a Binary Tree in Java](https://www.baeldung.com/java-binary-tree)

gson/src/main/java/org/baeldung/gson/primitives/models/BooleanExample.java

@@ -0,0 +1,9 @@
+package org.baeldung.gson.primitives.models;
+
+public class BooleanExample {
+    public boolean value;
+
+    public String toString() {
+        return "{boolean: " + value + "}";
+    }
+}

gson/src/main/java/org/baeldung/gson/primitives/models/ByteExample.java

@@ -0,0 +1,9 @@
+package org.baeldung.gson.primitives.models;
+
+public class ByteExample {
+    public byte value = (byte) 1;
+
+    public String toString() {
+        return "{byte: " + value + "}";
+    }
+}

gson/src/main/java/org/baeldung/gson/primitives/models/CharExample.java

@@ -0,0 +1,9 @@
+package org.baeldung.gson.primitives.models;
+
+public class CharExample {
+    public char value;
+
+    public String toString() {
+        return "{char: " + value + "}";
+    }
+}

gson/src/main/java/org/baeldung/gson/primitives/models/DoubleExample.java

@@ -0,0 +1,9 @@
+package org.baeldung.gson.primitives.models;
+
+public class DoubleExample {
+    public double value;
+
+    public String toString() {
+        return "{float: " + value + "}";
+    }
+}

gson/src/main/java/org/baeldung/gson/primitives/models/FloatExample.java

@@ -0,0 +1,9 @@
+package org.baeldung.gson.primitives.models;
+
+public class FloatExample {
+    public float value;
+
+    public String toString() {
+        return "{float: " + value + "}";
+    }
+}