Merge branch 'eugenp:master' into danielmcnally285_return_first_non_null

core-java-modules/core-java-8-datetime-2/src/main/java/com/baeldung/rounddate/RoundDate.java

@@ -0,0 +1,113 @@
+package com.baeldung.rounddate;
+
+import java.time.DayOfWeek;
+import java.time.temporal.ChronoField;
+import java.time.temporal.TemporalAdjusters;
+import java.util.Calendar;
+import java.util.Date;
+import java.time.LocalDateTime;
+import java.time.ZonedDateTime;
+
+public class RoundDate {
+    public static Date getDate(int year, int month, int day, int hour, int minute) {
+        Calendar calendar = Calendar.getInstance();
+        calendar.set(Calendar.YEAR, year);
+        calendar.set(Calendar.MONTH, month);
+        calendar.set(Calendar.DAY_OF_MONTH, day);
+        calendar.set(Calendar.HOUR_OF_DAY, hour);
+        calendar.set(Calendar.MINUTE, minute);
+        calendar.set(Calendar.SECOND, 0);
+        calendar.set(Calendar.MILLISECOND, 0);
+
+        return calendar.getTime();
+    }
+
+    public static Date roundToDay(Date date) {
+        Calendar calendar = Calendar.getInstance();
+        calendar.setTime(date);
+        calendar.set(Calendar.HOUR_OF_DAY, 0);
+        calendar.set(Calendar.MINUTE, 0);
+        calendar.set(Calendar.SECOND, 0);
+        calendar.set(Calendar.MILLISECOND, 0);
+        return calendar.getTime();
+    }
+
+    public static Date roundToNearestUnit(Date date, int unit) {
+        Calendar calendar = Calendar.getInstance();
+        calendar.setTime(date);
+
+        switch (unit) {
+            case Calendar.HOUR:
+                int minute = calendar.get(Calendar.MINUTE);
+                if (minute >= 0 && minute < 15) {
+                    calendar.set(Calendar.MINUTE, 0);
+                } else if (minute >= 15 && minute < 45) {
+                    calendar.set(Calendar.MINUTE, 30);
+                } else {
+                    calendar.set(Calendar.MINUTE, 0);
+                    calendar.add(Calendar.HOUR_OF_DAY, 1);
+                }
+                calendar.set(Calendar.SECOND, 0);
+                calendar.set(Calendar.MILLISECOND, 0);
+                break;
+
+            case Calendar.DAY_OF_MONTH:
+                int hour = calendar.get(Calendar.HOUR_OF_DAY);
+                if (hour >= 12) {
+                    calendar.add(Calendar.DAY_OF_MONTH, 1);
+                }
+                calendar.set(Calendar.HOUR_OF_DAY, 0);
+                calendar.set(Calendar.MINUTE, 0);
+                calendar.set(Calendar.SECOND, 0);
+                calendar.set(Calendar.MILLISECOND, 0);
+                break;
+
+            case Calendar.MONTH:
+                int day = calendar.get(Calendar.DAY_OF_MONTH);
+                if (day >= 15) {
+                    calendar.add(Calendar.MONTH, 1);
+                }
+                calendar.set(Calendar.DAY_OF_MONTH, 1);
+                calendar.set(Calendar.HOUR_OF_DAY, 0);
+                calendar.set(Calendar.MINUTE, 0);
+                calendar.set(Calendar.SECOND, 0);
+                calendar.set(Calendar.MILLISECOND, 0);
+                break;
+        }
+
+        return calendar.getTime();
+    }
+
+    public static LocalDateTime roundToStartOfMonthUsingLocalDateTime(LocalDateTime dateTime) {
+        return dateTime.withDayOfMonth(1).withHour(0).withMinute(0).withSecond(0).withNano(0);
+    }
+
+    public static LocalDateTime roundToEndOfWeekUsingLocalDateTime(LocalDateTime dateTime) {
+        return dateTime.with(TemporalAdjusters.next(DayOfWeek.SATURDAY))
+                .withHour(23)
+                .withMinute(59)
+                .withSecond(59)
+                .withNano(999);
+    }
+
+    public static ZonedDateTime roundToStartOfMonthUsingZonedDateTime(ZonedDateTime dateTime) {
+        return dateTime.withDayOfMonth(1)
+                .withHour(0)
+                .withMinute(0)
+                .withSecond(0)
+                .with(ChronoField.MILLI_OF_SECOND, 0)
+                .with(ChronoField.MICRO_OF_SECOND, 0)
+                .with(ChronoField.NANO_OF_SECOND, 0);
+    }
+
+    public static ZonedDateTime roundToEndOfWeekUsingZonedDateTime(ZonedDateTime dateTime) {
+        return dateTime.with(TemporalAdjusters.next(DayOfWeek.SATURDAY))
+                .withHour(23)
+                .withMinute(59)
+                .withSecond(59)
+                .with(ChronoField.MILLI_OF_SECOND, 999)
+                .with(ChronoField.MICRO_OF_SECOND, 999)
+                .with(ChronoField.NANO_OF_SECOND, 999);
+    }
+
+}

core-java-modules/core-java-8-datetime-2/src/test/java/com/baeldung/rounddate/DateRoundingUnitTest.java

@@ -0,0 +1,63 @@
+package com.baeldung.rounddate;
+
+import org.junit.Test;
+
+import java.time.LocalDateTime;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+import java.util.Calendar;
+import java.util.Date;
+
+import static org.junit.Assert.assertEquals;
+
+public class DateRoundingUnitTest {
+
+    @Test
+    public void givenDate_whenRoundToDay_thenBeginningOfDay() {
+        Date date = RoundDate.getDate(2023, Calendar.JANUARY, 27, 14, 30);
+        Date result = RoundDate.roundToDay(date);
+        assertEquals(RoundDate.getDate(2023, Calendar.JANUARY, 27, 0, 0), result);
+    }
+
+    @Test
+    public void givenDate_whenRoundToNearestUnit_thenNearestUnit() {
+        Date date = RoundDate.getDate(2023, Calendar.JANUARY, 27, 14, 12);
+        Date result = RoundDate.roundToNearestUnit(date, Calendar.DAY_OF_MONTH);
+        Date expected = RoundDate.getDate(2023, Calendar.JANUARY, 28, 0, 0);
+        assertEquals(expected, result);
+    }
+
+    @Test
+    public void givenLocalDateTime_whenRoundToStartOfMonth_thenStartOfMonth() {
+        LocalDateTime dateTime = LocalDateTime.of(2023, 1, 27, 14, 12);
+        LocalDateTime result = RoundDate.roundToStartOfMonthUsingLocalDateTime(dateTime);
+        LocalDateTime expected = LocalDateTime.of(2023, 1, 1, 0, 0, 0);
+        assertEquals(expected, result);
+    }
+
+
+    @Test
+    public void givenZonedDateTime_whenRoundToStartOfMonth_thenStartOfMonth() {
+        ZonedDateTime dateTime = ZonedDateTime.of(2023, 1, 27, 14, 12, 0, 0, ZoneId.systemDefault());
+        ZonedDateTime result = RoundDate.roundToStartOfMonthUsingZonedDateTime(dateTime);
+        ZonedDateTime expected = ZonedDateTime.of(2023, 1, 1, 0, 0, 0, 0, ZoneId.systemDefault());
+        assertEquals(expected, result);
+    }
+
+    @Test
+    public void givenLocalDateTime_whenRoundToEndOfWeek_thenEndOfWeek() {
+        LocalDateTime dateTime = LocalDateTime.of(2023, 1, 27, 14, 12);
+        LocalDateTime result = RoundDate.roundToEndOfWeekUsingLocalDateTime(dateTime);
+        LocalDateTime expected = LocalDateTime.of(2023, 1, 28, 23, 59, 59, 999);
+        assertEquals(expected, result);
+    }
+
+    @Test
+    public void givenZonedDateTime_whenRoundToEndOfWeek_thenEndOfWeek() {
+        ZonedDateTime dateTime = ZonedDateTime.of(2023, 1, 27, 14, 12, 0, 0, ZoneId.systemDefault());
+        ZonedDateTime result = RoundDate.roundToEndOfWeekUsingZonedDateTime(dateTime);
+        ZonedDateTime expected = ZonedDateTime.of(2023, 1, 28, 23, 59, 59, 999, ZoneId.systemDefault());
+        assertEquals(expected, result);
+    }
+
+}

core-java-modules/core-java-collections-5/src/test/java/com/baeldung/vectors/VectorOperationsUnitTest.java

@@ -0,0 +1,87 @@
+package com.baeldung.vectors;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Vector;
+
+import org.junit.Test;
+
+public class VectorOperationsUnitTest {
+
+    private static Vector<String> getVector() {
+        Vector<String> vector = new Vector<String>();
+        vector.add("Today");
+        vector.add("is");
+        vector.add("a");
+        vector.add("great");
+        vector.add("day!");
+
+        return vector;
+    }
+
+    @Test
+    public void givenAVector_whenAddElementsUsingAddMethod_thenElementsGetAddedAtEnd() {
+        Vector<String> vector = getVector();
+        vector.add("Hello");
+        assertEquals(6, vector.size());
+    }
+
+    @Test
+    public void givenAVector_whenUpdateElementAtIndex_thenElementAtIndexGetsUpdated() {
+        Vector<String> vector = getVector();
+        assertEquals(5, vector.size());
+        assertEquals("great", vector.get(3));
+        vector.set(3, "good");
+        assertEquals("good", vector.get(3));
+    }
+
+    @Test
+    public void givenAVector_whenRemoveAnElement_thenElementGetsRemovedFromTheVector() {
+        Vector<String> vector = getVector();
+        assertEquals(5, vector.size());
+
+        // remove a specific element
+        vector.remove("a");
+        assertEquals(4, vector.size());
+
+        // remove at specific index
+        vector.remove(2);
+        assertEquals("day!", vector.get(2));
+        assertEquals(3, vector.size());
+
+        assertEquals(false, vector.remove("SomethingThatDoesn'tExist"));
+    }
+
+    @Test(expected = ArrayIndexOutOfBoundsException.class)
+    public void givenAVector_whenIndexIsBeyondRange_thenRemoveMethodThrowsArrayIndexOutOfBoundsException() {
+        Vector<String> vector = getVector();
+        assertEquals(5, vector.size());
+        vector.remove(10);
+    }
+
+    @Test
+    public void givenAVector_whenGetElementWithinARange_thenGetMethodGetsAnElementFromTheVector() {
+        Vector<String> vector = getVector();
+        String fourthElement = vector.get(3);
+        assertEquals("great", fourthElement);
+    }
+
+    @Test(expected = ArrayIndexOutOfBoundsException.class)
+    public void givenAVector_whenGetElementBeyondARange_thenGetMethodThrowsArrayIndexOutOfBoundsException() {
+        Vector<String> vector = getVector();
+        assertEquals(5, vector.size());
+        vector.get(10);
+    }
+
+    @Test
+    public void givenAVector_whenAddElementFromACollection_thenAllElementsGetAdeddToTheVector() {
+        Vector<String> vector = getVector();
+        assertEquals(5, vector.size());
+        ArrayList<String> words = new ArrayList<>(Arrays.asList("Baeldung", "is", "cool!"));
+        vector.addAll(words);
+        assertEquals(8, vector.size());
+        assertEquals("cool!", vector.get(7));
+    }
+}

core-java-modules/core-java-collections-maps-7/pom.xml

@@ -79,5 +79,18 @@
             <version>1.5</version>
         </dependency>
     </dependencies>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <configuration>
+                    <argLine>
+                        --add-opens java.base/java.util=ALL-UNNAMED
+                    </argLine>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
 
 </project>

core-java-modules/core-java-collections-maps-7/src/test/java/com/baeldung/map/linkedhashmapfirstandlastentry/GetFirstAndLastEntryFromLinkedHashMapUnitTest.java

@@ -0,0 +1,85 @@
+package com.baeldung.map.linkedhashmapfirstandlastentry;
+
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Field;
+import java.util.Iterator;
+import java.util.LinkedHashMap;
+import java.util.Map.Entry;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+public class GetFirstAndLastEntryFromLinkedHashMapUnitTest {
+    private static final LinkedHashMap<String, String> THE_MAP = new LinkedHashMap<>();
+
+    static {
+        THE_MAP.put("key one", "a1 b1 c1");
+        THE_MAP.put("key two", "a2 b2 c2");
+        THE_MAP.put("key three", "a3 b3 c3");
+        THE_MAP.put("key four", "a4 b4 c4");
+    }
+
+    @Test
+    void whenIteratingEntrySet_thenGetExpectedResult() {
+        Entry<String, String> firstEntry = THE_MAP.entrySet().iterator().next();
+        assertEquals("key one", firstEntry.getKey());
+        assertEquals("a1 b1 c1", firstEntry.getValue());
+
+        Entry<String, String> lastEntry = null;
+        Iterator<Entry<String, String>> it = THE_MAP.entrySet().iterator();
+        while (it.hasNext()) {
+            lastEntry = it.next();
+        }
+
+        assertNotNull(lastEntry);
+        assertEquals("key four", lastEntry.getKey());
+        assertEquals("a4 b4 c4", lastEntry.getValue());
+
+    }
+
+    @Test
+    void whenConvertingEntriesToArray_thenGetExpectedResult() {
+
+        Entry<String, String>[] theArray = new Entry[THE_MAP.size()];
+        THE_MAP.entrySet().toArray(theArray);
+
+        Entry<String, String> firstEntry = theArray[0];
+        assertEquals("key one", firstEntry.getKey());
+        assertEquals("a1 b1 c1", firstEntry.getValue());
+
+        Entry<String, String> lastEntry = theArray[THE_MAP.size() - 1];
+        assertEquals("key four", lastEntry.getKey());
+        assertEquals("a4 b4 c4", lastEntry.getValue());
+    }
+
+    @Test
+    void whenUsingStreamAPI_thenGetExpectedResult() {
+        Entry<String, String> firstEntry = THE_MAP.entrySet().stream().findFirst().get();
+        assertEquals("key one", firstEntry.getKey());
+        assertEquals("a1 b1 c1", firstEntry.getValue());
+
+        Entry<String, String> lastEntry = THE_MAP.entrySet().stream().skip(THE_MAP.size() - 1).findFirst().get();
+
+        assertNotNull(lastEntry);
+        assertEquals("key four", lastEntry.getKey());
+        assertEquals("a4 b4 c4", lastEntry.getValue());
+    }
+
+    @Test
+    void whenUsingReflection_thenGetExpectedResult() throws NoSuchFieldException, IllegalAccessException {
+        Field head = THE_MAP.getClass().getDeclaredField("head");
+        head.setAccessible(true);
+        Entry<String, String> firstEntry = (Entry<String, String>) head.get(THE_MAP);
+        assertEquals("key one", firstEntry.getKey());
+        assertEquals("a1 b1 c1", firstEntry.getValue());
+
+        Field tail = THE_MAP.getClass().getDeclaredField("tail");
+        tail.setAccessible(true);
+        Entry<String, String> lastEntry = (Entry<String, String>) tail.get(THE_MAP);
+        assertEquals("key four", lastEntry.getKey());
+        assertEquals("a4 b4 c4", lastEntry.getValue());
+    }
+
+
+}

core-java-modules/core-java-documentation/src/main/java/com/baeldung/generictype/Pair.java

@@ -0,0 +1,23 @@
+package com.baeldung.generictype;
+
+/**
+ * @param <T> The type of the first value in the {@code Pair<T,S>}.
+ * @param <S> The type of the second value in the {@code Pair<T,S>}.
+ */
+
+public class Pair<T, S> {
+    public T first;
+    public S second;
+
+    /**
+     * Constructs a new Pair object with the specified values.
+     *
+     * @param a The first value.
+     * @param b The second value.
+     */
+
+    public Pair(T a, S b) {
+        first = a;
+        second = b;
+    }
+}

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

@@ -56,7 +56,7 @@
         <source.version>11</source.version>
         <target.version>11</target.version>
         <json.version>20200518</json.version>
-        <opencsv.version>4.1</opencsv.version>
+        <opencsv.version>5.8</opencsv.version>
     </properties>
 
 </project>

core-java-modules/core-java-jndi/src/test/java/com/baeldung/jndi/JndiNamingUnitTest.java

@@ -0,0 +1,72 @@
+package com.baeldung.jndi;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.springframework.jdbc.datasource.DriverManagerDataSource;
+import org.springframework.jndi.JndiTemplate;
+import org.springframework.mock.jndi.SimpleNamingContextBuilder;
+
+import javax.naming.*;
+import javax.sql.DataSource;
+
+import java.util.Enumeration;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class JndiNamingUnitTest {
+
+    private static InitialContext context;
+    private static DriverManagerDataSource dataSource;
+
+    @BeforeAll
+    static void setUp() throws Exception {
+        SimpleNamingContextBuilder builder = new SimpleNamingContextBuilder();
+        dataSource = new DriverManagerDataSource("jdbc:h2:mem:mydb");
+        builder.activate();
+
+        JndiTemplate jndiTemplate = new JndiTemplate();
+        context = (InitialContext) jndiTemplate.getContext();
+        
+        dataSource.setDriverClassName("org.h2.Driver");
+        context.bind("java:comp/env/jdbc/datasource", dataSource);
+    }
+
+    @Test
+    void givenACompositeName_whenAddingAnElement_thenNameIsAdded() throws Exception {
+        Name objectName = new CompositeName("java:comp/env/jdbc");
+
+        Enumeration<String> items = objectName.getAll();
+        while(items.hasMoreElements()) {
+            System.out.println(items.nextElement());
+        }
+
+        objectName.add("New Name");
+
+        assertEquals("env", objectName.get(1));
+        assertEquals("New Name", objectName.get(objectName.size() - 1));
+    }
+
+    @Test
+    void givenContext_whenLookupByName_thenReturnsValidObject() throws Exception {
+        DataSource ds = (DataSource) context.lookup("java:comp/env/jdbc/datasource");
+
+        assertNotNull(ds);
+        assertNotNull(ds.getConnection());
+    }
+    
+    @Test
+    void givenSubContext_whenLookupByName_thenReturnsValidObject() throws Exception {
+        Context subContext = (Context) context.lookup("java:comp/env");
+        DataSource ds = (DataSource) subContext.lookup("jdbc/datasource");
+
+        assertNotNull(ds);
+        assertNotNull(ds.getConnection());
+    }
+    
+    @AfterAll
+    static void tearDown() throws Exception {
+       context.close();
+    }
+
+}

core-java-modules/core-java-numbers-6/src/test/java/com/baeldung/genericnumberscomparator/GenericNumbersComparatorUnitTest.java

@@ -0,0 +1,122 @@
+package com.baeldung.genericnumberscomparator;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.lang.reflect.Method;
+import java.lang.reflect.Proxy;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+import java.util.function.BiFunction;
+import java.util.function.BiPredicate;
+import java.util.function.Function;
+
+import org.junit.jupiter.api.Test;
+
+class GenericNumbersComparatorUnitTest {
+
+    public int compareDouble(Number num1, Number num2) {
+        return Double.compare(num1.doubleValue(), num2.doubleValue());
+    }
+
+    @Test
+    void givenNumbers_whenUseCompareDouble_thenWillExecuteComparison() {
+        assertEquals(0, compareDouble(5, 5.0));
+    }
+
+    public int compareTo(Integer int1, Integer int2) {
+        return int1.compareTo(int2);
+    }
+
+    @Test
+    void givenNumbers_whenUseCompareTo_thenWillExecuteComparison() {
+        assertEquals(-1, compareTo(5, 7));
+    }
+
+    Map<Class<? extends Number>, BiFunction<Number, Number, Integer>> comparisonMap = new HashMap<>();
+
+    public int compareUsingMap(Number num1, Number num2) {
+        comparisonMap.put(Integer.class, (a, b) -> ((Integer) num1).compareTo((Integer) num2));
+
+        return comparisonMap.get(num1.getClass())
+            .apply(num1, num2);
+    }
+
+    @Test
+    void givenNumbers_whenUseCompareUsingMap_thenWillExecuteComparison() {
+        assertEquals(-1, compareUsingMap(5, 7));
+    }
+
+    public interface NumberComparator {
+        int compare(Number num1, Number num2);
+    }
+
+    @Test
+    void givenNumbers_whenUseProxy_thenWillExecuteComparison() {
+        NumberComparator proxy = (NumberComparator) Proxy.newProxyInstance(NumberComparator.class.getClassLoader(), new Class[] { NumberComparator.class },
+            (p, method, args) -> Double.compare(((Number) args[0]).doubleValue(), ((Number) args[1]).doubleValue()));
+        assertEquals(0, proxy.compare(5, 5.0));
+    }
+
+    public int compareUsingReflection(Number num1, Number num2) throws Exception {
+        Method method = num1.getClass()
+            .getMethod("compareTo", num1.getClass());
+        return (int) method.invoke(num1, num2);
+    }
+
+    @Test
+    void givenNumbers_whenUseCompareUsingReflection_thenWillExecuteComparison() throws Exception {
+        assertEquals(-1, compareUsingReflection(5, 7));
+    }
+
+    interface NumberComparatorFactory {
+        Comparator<Number> getComparator();
+    }
+
+    class IntegerComparatorFactory implements NumberComparatorFactory {
+        @Override
+        public Comparator<Number> getComparator() {
+            return (num1, num2) -> ((Integer) num1).compareTo((Integer) num2);
+        }
+    }
+
+    @Test
+    void givenNumbers_whenUseComparatorFactory_thenWillExecuteComparison() {
+        NumberComparatorFactory factory = new IntegerComparatorFactory();
+        Comparator<Number> comparator = factory.getComparator();
+        assertEquals(-1, comparator.compare(5, 7));
+    }
+
+    Function<Number, Double> toDouble = Number::doubleValue;
+    BiPredicate<Number, Number> isEqual = (num1, num2) -> toDouble.apply(num1)
+        .equals(toDouble.apply(num2));
+
+    @Test
+    void givenNumbers_whenUseIsEqual_thenWillExecuteComparison() {
+        assertEquals(true, isEqual.test(5, 5.0));
+    }
+
+    private Number someNumber = 5;
+    private Number anotherNumber = 5.0;
+
+    Optional<Number> optNum1 = Optional.ofNullable(someNumber);
+    Optional<Number> optNum2 = Optional.ofNullable(anotherNumber);
+    int comparisonResult = optNum1.flatMap(n1 -> optNum2.map(n2 -> Double.compare(n1.doubleValue(), n2.doubleValue())))
+        .orElse(0);
+
+    @Test
+    void givenNumbers_whenUseComparisonResult_thenWillExecuteComparison() {
+        assertEquals(0, comparisonResult);
+    }
+
+    private boolean someCondition = true;
+    Function<Number, ?> dynamicFunction = someCondition ? Number::doubleValue : Number::intValue;
+    Comparator<Number> dynamicComparator = (num1, num2) -> ((Comparable) dynamicFunction.apply(num1)).compareTo(dynamicFunction.apply(num2));
+
+    @Test
+    void givenNumbers_whenUseDynamicComparator_thenWillExecuteComparison() {
+        assertEquals(0, dynamicComparator.compare(5, 5.0));
+    }
+
+}

core-java-modules/core-java-records/src/main/java/com/baeldung/optionalsasparameterrecords/Product.java

@@ -0,0 +1,6 @@
+package com.baeldung.optionalsasparameterrecords;
+
+import java.util.Optional;
+
+public record Product(String name, double price, Optional<String> description) {
+}

core-java-modules/core-java-records/src/test/java/com/baeldung/optionalsasparameterrecords/OptionalAsRecordParameterUnitTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.optionalsasparameterrecords;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+
+public class OptionalAsRecordParameterUnitTest {
+
+    @Test
+    public void givenRecordCreationWithOptional_thenCreateItProperly() {
+        var emptyDescriptionProduct = new Product("television", 1699.99, Optional.empty());
+        Assertions.assertEquals("television", emptyDescriptionProduct.name());
+        Assertions.assertEquals(1699.99, emptyDescriptionProduct.price());
+        Assertions.assertNull(emptyDescriptionProduct.description().orElse(null));
+    }
+}

core-java-modules/core-java-streams-5/src/test/java/com/baeldung/streamtomapandmultimap/StreamToMapAndMultiMapUnitTest.java

@@ -0,0 +1,100 @@
+package com.baeldung.streamtomapandmultimap;
+
+import com.google.common.collect.LinkedHashMultimap;
+import org.junit.Test;
+
+import java.util.*;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static org.junit.Assert.assertEquals;
+
+public class StreamToMapAndMultiMapUnitTest {
+    @Test
+    public void givenStringStream_whenConvertingToMapWithMerge_thenExpectedMapIsGenerated() {
+        Stream<String> stringStream = Stream.of("one", "two", "three", "two");
+
+        Map<String, String> mergedMap = stringStream.collect(
+                Collectors.toMap(s -> s, s -> s, (s1, s2) -> s1 + ", " + s2)
+        );
+
+        // Define the expected map
+        Map<String, String> expectedMap = Map.of(
+                "one", "one",
+                "two", "two, two",
+                "three", "three"
+        );
+
+        assertEquals(expectedMap, mergedMap);
+    }
+
+    @Test
+    public void givenStringStream_whenConvertingToMultimap_thenExpectedMultimapIsGenerated() {
+        Stream<String> stringStream = Stream.of("one", "two", "three", "two");
+
+        LinkedHashMultimap<Object, Object> multimap = LinkedHashMultimap.create();
+
+        stringStream.collect(Collectors.groupingBy(
+                s -> s,
+                Collectors.mapping(s -> s, Collectors.toList())
+        )).forEach((key, value) -> multimap.putAll(key, value));
+
+        LinkedHashMultimap<Object, Object> expectedMultimap = LinkedHashMultimap.create();
+        expectedMultimap.put("one", "one");
+        expectedMultimap.put("two", "two");
+        expectedMultimap.put("three", "three");
+
+        assertEquals(expectedMultimap, multimap);
+    }
+
+    @Test
+    public void givenStringStream_whenConvertingToMultimapWithStreamReduce_thenExpectedMultimapIsGenerated() {
+        Stream<String> stringStream = Stream.of("one", "two", "three", "two");
+
+        Map<String, List<String>> multimap = stringStream.reduce(
+                new HashMap<>(),
+                (map, element) -> {
+                    map.computeIfAbsent(element, k -> new ArrayList<>()).add(element);
+                    return map;
+                },
+                (map1, map2) -> {
+                    map2.forEach((key, value) -> map1.merge(key, value, (list1, list2) -> {
+                        list1.addAll(list2);
+                        return list1;
+                    }));
+                    return map1;
+                }
+        );
+
+        Map<String, List<String>> expectedMultimap = new HashMap<>();
+        expectedMultimap.put("one", Collections.singletonList("one"));
+        expectedMultimap.put("two", Arrays.asList("two", "two"));
+        expectedMultimap.put("three", Collections.singletonList("three"));
+
+        assertEquals(expectedMultimap, multimap);
+    }
+
+    @Test
+    public void givenStringStream_whenConvertingToMapWithStreamReduce_thenExpectedMapIsGenerated() {
+        Stream<String> stringStream = Stream.of("one", "two", "three", "two");
+
+        Map<String, String> resultMap = stringStream.reduce(
+                new HashMap<>(),
+                (map, element) -> {
+                    map.put(element, element);
+                    return map;
+                },
+                (map1, map2) -> {
+                    map1.putAll(map2);
+                    return map1;
+                }
+        );
+
+        Map<String, String> expectedMap = new HashMap<>();
+        expectedMap.put("one", "one");
+        expectedMap.put("two", "two");
+        expectedMap.put("three", "three");
+
+        assertEquals(expectedMap, resultMap);
+    }
+}

core-java-modules/core-java-streams-simple/src/test/java/com/baeldung/streams/Java8StreamsUnitTest.java

@@ -1,7 +1,11 @@
 package com.baeldung.streams;
 
-import org.junit.Before;
-import org.junit.Test;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
 
 import java.nio.file.Path;
 import java.nio.file.Paths;
@@ -11,14 +15,12 @@ import java.util.List;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
-import static org.junit.Assert.*;
+class Java8StreamsUnitTest {
 
-public class Java8StreamsUnitTest {
+    private static List<String> list;
 
-    private List<String> list;
-
-    @Before
-    public void init() {
+    @BeforeAll
+    public static void init() {
         list = new ArrayList<>();
         list.add("One");
         list.add("OneAndOnly");
@@ -42,60 +44,73 @@ public class Java8StreamsUnitTest {
         Stream<String> streamOf = Stream.of("a", "b", "c");
         assertEquals(streamOf.count(), 3);
 
-        long count = list.stream().distinct().count();
+        long count = list.stream()
+            .distinct()
+            .count();
         assertEquals(count, 9);
     }
 
     @Test
-    public void checkStreamCount_whenOperationFilter_thanCorrect() {
-        Stream<String> streamFilter = list.stream().filter(element -> element.isEmpty());
+    void checkStreamCount_whenOperationFilter_thanCorrect() {
+        Stream<String> streamFilter = list.stream()
+            .filter(element -> element.isEmpty());
         assertEquals(streamFilter.count(), 2);
     }
 
     @Test
-    public void checkStreamCount_whenOperationMap_thanCorrect() {
+    void checkStreamCount_whenOperationMap_thanCorrect() {
         List<String> uris = new ArrayList<>();
         uris.add("C:\\My.txt");
-        Stream<Path> streamMap = uris.stream().map(uri -> Paths.get(uri));
+        Stream<Path> streamMap = uris.stream()
+            .map(uri -> Paths.get(uri));
         assertEquals(streamMap.count(), 1);
 
         List<Detail> details = new ArrayList<>();
         details.add(new Detail());
         details.add(new Detail());
-        Stream<String> streamFlatMap = details.stream().flatMap(detail -> detail.getParts().stream());
+        Stream<String> streamFlatMap = details.stream()
+            .flatMap(detail -> detail.getParts()
+                .stream());
         assertEquals(streamFlatMap.count(), 4);
     }
 
     @Test
-    public void checkStreamCount_whenOperationMatch_thenCorrect() {
-        boolean isValid = list.stream().anyMatch(element -> element.contains("h"));
-        boolean isValidOne = list.stream().allMatch(element -> element.contains("h"));
-        boolean isValidTwo = list.stream().noneMatch(element -> element.contains("h"));
+    void checkStreamCount_whenOperationMatch_thenCorrect() {
+        boolean isValid = list.stream()
+            .anyMatch(element -> element.contains("h"));
+        boolean isValidOne = list.stream()
+            .allMatch(element -> element.contains("h"));
+        boolean isValidTwo = list.stream()
+            .noneMatch(element -> element.contains("h"));
         assertTrue(isValid);
         assertFalse(isValidOne);
         assertFalse(isValidTwo);
     }
 
     @Test
-    public void checkStreamReducedValue_whenOperationReduce_thenCorrect() {
+    void checkStreamReducedValue_whenOperationReduce_thenCorrect() {
         List<Integer> integers = new ArrayList<>();
         integers.add(1);
         integers.add(1);
         integers.add(1);
-        Integer reduced = integers.stream().reduce(23, (a, b) -> a + b);
+        Integer reduced = integers.stream()
+            .reduce(23, (a, b) -> a + b);
         assertTrue(reduced == 26);
     }
 
     @Test
-    public void checkStreamContains_whenOperationCollect_thenCorrect() {
-        List<String> resultList = list.stream().map(element -> element.toUpperCase()).collect(Collectors.toList());
+    void checkStreamContains_whenOperationCollect_thenCorrect() {
+        List<String> resultList = list.stream()
+            .map(element -> element.toUpperCase())
+            .collect(Collectors.toList());
         assertEquals(resultList.size(), list.size());
         assertTrue(resultList.contains(""));
     }
 
     @Test
     public void checkParallelStream_whenDoWork() {
-        list.parallelStream().forEach(element -> doWork(element));
+        list.parallelStream()
+            .forEach(element -> doWork(element));
     }
 
     private void doWork(String string) {

core-java-modules/core-java-string-operations-4/pom.xml

@@ -58,7 +58,7 @@
     <properties>
         <maven.compiler.source>11</maven.compiler.source>
         <maven.compiler.target>11</maven.compiler.target>
-        <opencsv.version>4.1</opencsv.version>
+        <opencsv.version>5.8</opencsv.version>
         <spring-core.version>5.3.13</spring-core.version>
         <apache-commons-lang3.version>3.12.0</apache-commons-lang3.version>
         <apache-commons-text.version>1.10.0</apache-commons-text.version>

core-java-modules/core-java-string-operations-4/src/main/java/com/baeldung/commaseparatedstring/SplitCommaSeparatedString.java

@@ -12,6 +12,7 @@ import com.opencsv.CSVParser;
 import com.opencsv.CSVParserBuilder;
 import com.opencsv.CSVReader;
 import com.opencsv.CSVReaderBuilder;
+import com.opencsv.exceptions.CsvException;
 
 public class SplitCommaSeparatedString {
 
@@ -50,7 +51,7 @@ public class SplitCommaSeparatedString {
         return splitter.splitToList(input);
     }
 
-    public static List<String[]> splitMultiLineWithOpenCSV(String input) throws IOException {
+    public static List<String[]> splitMultiLineWithOpenCSV(String input) throws IOException, CsvException {
         CSVParser parser = new CSVParserBuilder().withSeparator(',')
             .build();
 

core-java-modules/core-java-string-operations-4/src/test/java/com/baeldung/commaseparatedstring/SplitCommaSeparatedStringUnitTest.java

@@ -14,6 +14,8 @@ import java.util.List;
 
 import org.junit.Test;
 
+import com.opencsv.exceptions.CsvException;
+
 public class SplitCommaSeparatedStringUnitTest {
     
     @Test
@@ -27,7 +29,7 @@ public class SplitCommaSeparatedStringUnitTest {
     }
     
     @Test
-    public void givenMultiLineInput_whenParsing_shouldIgnoreCommasInsideDoubleQuotes() throws IOException {
+    public void givenMultiLineInput_whenParsing_shouldIgnoreCommasInsideDoubleQuotes() throws IOException, CsvException {
         String input = "baeldung,tutorial,splitting,text,\"ignoring this comma,\"" + System.lineSeparator()
         + "splitting,a,regular,line,no double quotes";
 

core-java-modules/core-java-string-operations-7/src/main/java/com/baeldung/mutablestrings/CharsetUsageExample.java

@@ -0,0 +1,34 @@
+package com.baeldung.mutablestrings;
+
+import java.nio.ByteBuffer;
+import java.nio.CharBuffer;
+import java.nio.charset.CharacterCodingException;
+import java.nio.charset.Charset;
+import java.nio.charset.CharsetDecoder;
+import java.nio.charset.CharsetEncoder;
+import java.nio.charset.CoderResult;
+
+public class CharsetUsageExample {
+
+    public ByteBuffer encodeString(String inputString) {
+        Charset charset = Charset.forName("UTF-8");
+        CharsetEncoder encoder = charset.newEncoder();
+
+        CharBuffer charBuffer = CharBuffer.wrap(inputString);
+        ByteBuffer byteBuffer = ByteBuffer.allocate(50);
+
+        encoder.encode(charBuffer, byteBuffer, true); // true indicates the end of input
+        byteBuffer.flip();
+        return byteBuffer;
+    }
+
+    public String decodeString(ByteBuffer byteBuffer) {
+        Charset charset = Charset.forName("UTF-8");
+        CharsetDecoder decoder = charset.newDecoder();
+        CharBuffer decodedCharBuffer = CharBuffer.allocate(50);
+        decoder.decode(byteBuffer, decodedCharBuffer, true);
+        decodedCharBuffer.flip();
+
+        return decodedCharBuffer.toString();
+    }
+}

core-java-modules/core-java-string-operations-7/src/main/java/com/baeldung/mutablestrings/MutableStringUsingCharset.java

@@ -0,0 +1,65 @@
+package com.baeldung.mutablestrings;
+
+import java.nio.ByteBuffer;
+import java.nio.CharBuffer;
+import java.nio.charset.Charset;
+import java.nio.charset.CharsetDecoder;
+import java.nio.charset.CharsetEncoder;
+import java.nio.charset.CoderResult;
+import java.util.concurrent.atomic.AtomicReference;
+
+public class MutableStringUsingCharset {
+
+    private final AtomicReference<CharBuffer> cbRef = new AtomicReference<>();
+    private final Charset myCharset = new Charset("mycharset", null) {
+        @Override
+        public boolean contains(Charset cs) {
+            return false;
+        }
+
+        @Override
+        public CharsetDecoder newDecoder() {
+            return new CharsetDecoder(this, 1.0f, 1.0f) {
+                @Override
+                protected CoderResult decodeLoop(ByteBuffer in, CharBuffer out) {
+                    cbRef.set(out);
+                    while (in.remaining() > 0) {
+                        out.append((char) in.get());
+                    }
+                    return CoderResult.UNDERFLOW;
+                }
+            };
+        }
+
+        @Override
+        public CharsetEncoder newEncoder() {
+            CharsetEncoder cd = new CharsetEncoder(this, 1.0f, 1.0f) {
+                @Override
+                protected CoderResult encodeLoop(CharBuffer in, ByteBuffer out) {
+                    while (in.hasRemaining()) {
+                        if (!out.hasRemaining()) {
+                            return CoderResult.OVERFLOW;
+                        }
+                        char currentChar = in.get();
+                        if (currentChar > 127) {
+                            return CoderResult.unmappableForLength(1);
+                        }
+                        out.put((byte) currentChar);
+                    }
+                    return CoderResult.UNDERFLOW;
+                }
+            };
+            return cd;
+        }
+    };
+
+    public String createModifiableString(String s) {
+        return new String(s.getBytes(), myCharset);
+    }
+
+    public void modifyString() {
+        CharBuffer cb = cbRef.get();
+        cb.position(0);
+        cb.put("xyz");
+    }
+}

core-java-modules/core-java-string-operations-7/src/main/java/com/baeldung/mutablestrings/MutableStrings.java

@@ -0,0 +1,24 @@
+package com.baeldung.mutablestrings;
+
+import java.lang.reflect.Field;
+import java.nio.charset.Charset;
+
+import com.google.errorprone.annotations.DoNotCall;
+
+public class MutableStrings {
+
+    /**
+     * This involves using Reflection to change String fields and it is not encouraged to use this in programs.
+     * @throws NoSuchFieldException
+     * @throws IllegalAccessException
+     */
+    @DoNotCall
+    public void mutableUsingReflection() throws NoSuchFieldException, IllegalAccessException {
+        String myString = "Hello World";
+        String otherString = new String("Hello World");
+        Field f = String.class.getDeclaredField("value");
+        f.setAccessible(true);
+        f.set(myString, "Hi World".toCharArray());
+        System.out.println(otherString);
+    }
+}

core-java-modules/core-java-string-operations-7/src/test/java/com/baeldung/mutablestring/CharsetUsageUnitTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.mutablestring;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import com.baeldung.mutablestrings.CharsetUsageExample;
+
+public class CharsetUsageUnitTest {
+
+    @Test
+    public void givenCharset_whenStringIsEncodedAndDecoded_thenGivesCorrectResult() {
+        CharsetUsageExample ch = new CharsetUsageExample();
+        String inputString = "hello दुनिया";
+        String result = ch.decodeString(ch.encodeString(inputString));
+        Assertions.assertEquals(inputString, result);
+    }
+}

core-java-modules/core-java-string-operations-7/src/test/java/com/baeldung/mutablestring/MutableStringUsingCharsetUnitTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.mutablestring;
+
+import org.junit.Assert;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+import com.baeldung.mutablestrings.MutableStringUsingCharset;
+
+public class MutableStringUsingCharsetUnitTest {
+    @Test
+    @Disabled
+    /**
+     * This test is disabled as it works well for Java 8 and below
+     */
+    public void givenCustomCharSet_whenStringUpdated_StringGetsMutated() throws Exception {
+        MutableStringUsingCharset ms = new MutableStringUsingCharset();
+        String s = ms.createModifiableString("Hello");
+        Assert.assertEquals("Hello", s);
+        ms.modifyString();
+        Assert.assertEquals("something", s);
+    }
+
+}
+

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

@@ -14,3 +14,4 @@ Listed here there are only those articles that does not fit into other core-java
 - [Java String Interview Questions and Answers](https://www.baeldung.com/java-string-interview-questions)
 - [Java Multi-line String](https://www.baeldung.com/java-multiline-string)
 - [Reuse StringBuilder for Efficiency](https://www.baeldung.com/java-reuse-stringbuilder-for-efficiency)
+- [How to Iterate Over the String Characters in Java](https://www.baeldung.com/java-iterate-string-characters)

core-java-modules/core-java-strings/src/main/java/com/baeldung/stringIterator/StringIterator.java

@@ -0,0 +1,42 @@
+package com.baeldung.stringIterator;
+
+import java.text.*; 
+import java.util.*;
+
+public class StringIterator {
+
+    public static String javaCharArray(String str){
+        StringBuilder result = new StringBuilder();
+        for (char c : str.toCharArray()) { 
+            result.append(c);
+        }
+        return result.toString();
+    }
+
+    public static String javaforLoop(String str) {
+        StringBuilder result = new StringBuilder();
+        for (int i = 0; i < str.length(); i++) {
+            char c = str.charAt(i);
+            result.append(c);
+        }
+        return result.toString();
+    }
+
+    public static String java8forEach(String str){
+        StringBuilder result = new StringBuilder();
+        str.chars().forEach(name -> {
+            result.append((char) name);
+        });
+        return result.toString();
+    }
+
+    public static String javaCharacterIterator(String str){
+        StringBuilder result = new StringBuilder();
+        CharacterIterator it = new StringCharacterIterator(str);  
+        while (it.current() != CharacterIterator.DONE) { 
+            result.append(it.current()); 
+            it.next(); 
+        }
+        return result.toString();
+    }
+}

core-java-modules/core-java-strings/src/test/java/com/baeldung/stringIterator/StringIteratorTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.stringIterator;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+public class StringIteratorTest {
+  
+    @Test
+    public void whenUseCharArrayMethod_thenIterate() {
+        String input = "Hello, Baeldung!";
+        String expectedOutput = "Hello, Baeldung!";
+        String result = StringIterator.javaCharArray(input);
+        assertEquals(expectedOutput, result);
+    }
+  
+    @Test
+    public void whenUseJavaForLoop_thenIterate() {
+        String input = "Hello, Baeldung!";
+        String expectedOutput = "Hello, Baeldung!";
+        String result = StringIterator.javaForLoop(input);
+        assertEquals(expectedOutput, result);
+    }
+  
+    @Test
+    public void whenUseForEachMethod_thenIterate() {
+        String input = "Hello, Baeldung!";
+        String expectedOutput = "Hello, Baeldung!";
+        String result = StringIterator.java8ForEach(input);
+        assertEquals(expectedOutput, result);
+    }
+  
+    @Test
+    public void whenUseCharacterIterator_thenIterate() {
+        String input = "Hello, Baeldung!";
+        String expectedOutput = "Hello, Baeldung!";
+        String result = StringIterator.javaCharacterIterator(input);
+        assertEquals(expectedOutput, result);
+    }
+}

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

@@ -0,0 +1,11 @@
+## JNI
+
+This module contains articles about the Java Native Interface (JNI).
+
+### Relevant Articles: 
+
+- [Guide to JNI (Java Native Interface)](https://www.baeldung.com/jni)
+- [Using JNA to Access Native Dynamic Libraries](https://www.baeldung.com/java-jna-dynamic-libraries)
+- [Check if a Java Program Is Running in 64-Bit or 32-Bit JVM](https://www.baeldung.com/java-detect-jvm-64-or-32-bit)
+- [How to use JNI’s RegisterNatives() method?](https://www.baeldung.com/jni-registernatives)
+- [Custom DLL Load – Fixing the “java.lang.UnsatisfiedLinkError” Error](https://www.baeldung.com/java-custom-dll-load-fixing-the-java-lang-unsatisfiedlinkerror-error)

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

@@ -0,0 +1,40 @@
+<?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>java-native</artifactId>
+    <name>java-native</name>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>net.java.dev.jna</groupId>
+            <artifactId>jna-platform</artifactId>
+            <version>${jna.version}</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <configuration>
+                    <!-- we don't want to reuse JVMs here ! -->
+                    <reuseForks>false</reuseForks>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <jna.version>5.6.0</jna.version>
+    </properties>
+
+</project>

core-java-modules/java-native/src/main/cpp/com_baeldung_jni_ExampleObjectsJNI.cpp

@@ -0,0 +1,48 @@
+#include "com_baeldung_jni_ExampleObjectsJNI.h"
+#include <iostream>
+
+/*
+ * Class:     com_baeldung_jni_ExampleObjectsJNI
+ * Method:    createUser
+ * Signature: (Ljava/lang/String;D)Lcom/baeldung/jni/UserData;
+ */
+JNIEXPORT jobject JNICALL Java_com_baeldung_jni_ExampleObjectsJNI_createUser
+  (JNIEnv *env, jobject thisObject, jstring name, jdouble balance){
+  
+    // Create the object of the class UserData
+    jclass userDataClass = env->FindClass("com/baeldung/jni/UserData");
+    jobject newUserData = env->AllocObject(userDataClass);
+	
+    // Get UserData fields to set
+    jfieldID nameField = env->GetFieldID(userDataClass , "name", "Ljava/lang/String;");
+    jfieldID balanceField = env->GetFieldID(userDataClass , "balance", "D");
+	
+    // Set the values of the new object
+    env->SetObjectField(newUserData, nameField, name);
+    env->SetDoubleField(newUserData, balanceField, balance);
+    
+    // Return the created object
+    return newUserData;
+  }
+
+/*
+ * Class:     com_baeldung_jni_ExampleObjectsJNI
+ * Method:    printUserData
+ * Signature: (Lcom/baeldung/jni/UserData;)Ljava/lang/String;
+ */
+JNIEXPORT jstring JNICALL Java_com_baeldung_jni_ExampleObjectsJNI_printUserData
+  (JNIEnv *env, jobject thisObject, jobject userData){
+  	
+  	// Find the class method id
+  	jclass userDataClass = env->GetObjectClass(userData);
+  	jmethodID methodId = env->GetMethodID(userDataClass, "getUserInfo", "()Ljava/lang/String;");
+
+    // Call the object method and get the result
+    jstring result = (jstring)env->CallObjectMethod(userData, methodId);
+	
+    // Print the result
+    std::cout << "C++: User data is: " << env->GetStringUTFChars(result, NULL) << std::endl;
+    
+    return result;
+  }
+

core-java-modules/java-native/src/main/cpp/com_baeldung_jni_ExampleObjectsJNI.h

@@ -0,0 +1,29 @@
+/* DO NOT EDIT THIS FILE - it is machine generated */
+#include <jni.h>
+/* Header for class com_baeldung_jni_ExampleObjectsJNI */
+
+#ifndef _Included_com_baeldung_jni_ExampleObjectsJNI
+#define _Included_com_baeldung_jni_ExampleObjectsJNI
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*
+ * Class:     com_baeldung_jni_ExampleObjectsJNI
+ * Method:    createUser
+ * Signature: (Ljava/lang/String;D)Lcom/baeldung/jni/UserData;
+ */
+JNIEXPORT jobject JNICALL Java_com_baeldung_jni_ExampleObjectsJNI_createUser
+  (JNIEnv *, jobject, jstring, jdouble);
+
+/*
+ * Class:     com_baeldung_jni_ExampleObjectsJNI
+ * Method:    printUserData
+ * Signature: (Lcom/baeldung/jni/UserData;)V
+ */
+JNIEXPORT jstring JNICALL Java_com_baeldung_jni_ExampleObjectsJNI_printUserData
+  (JNIEnv *, jobject, jobject);
+
+#ifdef __cplusplus
+}
+#endif
+#endif

core-java-modules/java-native/src/main/cpp/com_baeldung_jni_ExampleParametersJNI.cpp

@@ -0,0 +1,34 @@
+#include "com_baeldung_jni_ExampleParametersJNI.h"
+#include <iostream>
+#include <string>
+
+/*
+ * Class:     com_baeldung_jni_ExampleParametersJNI
+ * Method:    sumIntegers
+ * Signature: (II)J
+ */
+JNIEXPORT jlong JNICALL Java_com_baeldung_jni_ExampleParametersJNI_sumIntegers (JNIEnv* env, jobject thisObject, jint first, jint second){
+    std::cout << "C++: The numbers received are : " << first << " and " << second << std::endl;
+    return (long)first + (long)second;
+}
+
+
+/*
+ * Class:     com_baeldung_jni_ExampleParametersJNI
+ * Method:    sayHelloToMe
+ * Signature: (Ljava/lang/String;Z)Ljava/lang/String;
+ */
+JNIEXPORT jstring JNICALL Java_com_baeldung_jni_ExampleParametersJNI_sayHelloToMe (JNIEnv* env, jobject thisObject, jstring name, jboolean isFemale){
+    const char* nameCharPointer = env->GetStringUTFChars(name, NULL);
+    std::cout << "C++: The string received is: " << nameCharPointer << std::endl;
+    std::string title;
+    if(isFemale){
+        title = "Ms. ";
+    }
+    else{
+        title = "Mr. ";
+    }
+
+    std::string fullName = title + nameCharPointer;
+    return env->NewStringUTF(fullName.c_str());
+}

core-java-modules/java-native/src/main/cpp/com_baeldung_jni_ExampleParametersJNI.h

@@ -0,0 +1,29 @@
+/* DO NOT EDIT THIS FILE - it is machine generated */
+#include <jni.h>
+/* Header for class com_baeldung_jni_ExampleParametersJNI */
+
+#ifndef _Included_com_baeldung_jni_ExampleParametersJNI
+#define _Included_com_baeldung_jni_ExampleParametersJNI
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*
+ * Class:     com_baeldung_jni_ExampleParametersJNI
+ * Method:    sumIntegers
+ * Signature: (II)J
+ */
+JNIEXPORT jlong JNICALL Java_com_baeldung_jni_ExampleParametersJNI_sumIntegers
+  (JNIEnv*, jobject, jint, jint);
+
+/*
+ * Class:     com_baeldung_jni_ExampleParametersJNI
+ * Method:    sayHelloToMe
+ * Signature: (Ljava/lang/String;Z)Ljava/lang/String;
+ */
+JNIEXPORT jstring JNICALL Java_com_baeldung_jni_ExampleParametersJNI_sayHelloToMe
+  (JNIEnv*, jobject, jstring, jboolean);
+
+#ifdef __cplusplus
+}
+#endif
+#endif

core-java-modules/java-native/src/main/cpp/com_baeldung_jni_HelloWorldJNI.cpp

@@ -0,0 +1,13 @@
+#include "com_baeldung_jni_HelloWorldJNI.h"
+#include <iostream>
+
+/*
+ * Class:     com_baeldung_jni_HelloWorldJNI
+ * Method:    sayHello
+ * Signature: ()Ljava/lang/String;
+ */
+JNIEXPORT jstring JNICALL Java_com_baeldung_jni_HelloWorldJNI_sayHello (JNIEnv* env, jobject thisObject) {
+	std::string hello = "Hello from C++ !!";
+    std::cout << hello << std::endl;
+    return env->NewStringUTF(hello.c_str());
+}

core-java-modules/java-native/src/main/cpp/com_baeldung_jni_HelloWorldJNI.h

@@ -0,0 +1,21 @@
+/* DO NOT EDIT THIS FILE - it is machine generated */
+#include <jni.h>
+/* Header for class com_baeldung_jni_HelloWorldJNI */
+
+#ifndef _Included_com_baeldung_jni_HelloWorldJNI
+#define _Included_com_baeldung_jni_HelloWorldJNI
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*
+ * Class:     com_baeldung_jni_HelloWorldJNI
+ * Method:    sayHello
+ * Signature: ()V
+ */
+JNIEXPORT jstring JNICALL Java_com_baeldung_jni_HelloWorldJNI_sayHello
+  (JNIEnv *, jobject);
+
+#ifdef __cplusplus
+}
+#endif
+#endif

core-java-modules/java-native/src/main/cpp/com_baeldung_jni_RegisterNativesHelloWorldJNI.cpp

@@ -0,0 +1,21 @@
+#include "com_baeldung_jni_RegisterNativesHelloWorldJNI.h"
+#include <iostream>
+
+
+JNIEXPORT jstring JNICALL hello (JNIEnv* env, jobject thisObject) {
+    std::string hello = "Hello from registered native C++ !!";
+    std::cout << hello << std::endl;
+    return env->NewStringUTF(hello.c_str());
+}
+
+static JNINativeMethod methods[] = {
+  {"sayHello", "()Ljava/lang/String;", (void*) &hello },
+};
+
+
+JNIEXPORT void JNICALL Java_com_baeldung_jni_RegisterNativesHelloWorldJNI_register (JNIEnv* env, jobject thsObject) {
+    jclass clazz = env->FindClass("com/baeldung/jni/RegisterNativesHelloWorldJNI");
+
+    (env)->RegisterNatives(clazz, methods, sizeof(methods)/sizeof(methods[0]));
+}
+

core-java-modules/java-native/src/main/cpp/com_baeldung_jni_RegisterNativesHelloWorldJNI.h

@@ -0,0 +1,29 @@
+/* DO NOT EDIT THIS FILE - it is machine generated */
+#include <jni.h>
+/* Header for class com_baeldung_jni_RegisterNativesHelloWorldJNI */
+
+#ifndef _Included_com_baeldung_jni_RegisterNativesHelloWorldJNI
+#define _Included_com_baeldung_jni_RegisterNativesHelloWorldJNI
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*
+ * Class:     com_baeldung_jni_RegisterNativesHelloWorldJNI
+ * Method:    sayHello
+ * Signature: ()Ljava/lang/String;
+ */
+JNIEXPORT jstring JNICALL Java_com_baeldung_jni_RegisterNativesHelloWorldJNI_sayHello
+  (JNIEnv *, jobject);
+
+/*
+ * Class:     com_baeldung_jni_RegisterNativesHelloWorldJNI
+ * Method:    register
+ * Signature: ()V
+ */
+JNIEXPORT void JNICALL Java_com_baeldung_jni_RegisterNativesHelloWorldJNI_register
+  (JNIEnv *, jobject);
+
+#ifdef __cplusplus
+}
+#endif
+#endif

core-java-modules/java-native/src/main/cpp/generateNativeLib.bat

@@ -0,0 +1,6 @@
+REM Create the header with javac -h . ClassName.java
+REM Remember to set your JAVA_HOME env var
+g++ -c -I%JAVA_HOME%\include -I%JAVA_HOME%\include\win32 com_baeldung_jni_HelloWorldJNI.cpp -o com_baeldung_jni_HelloWorldJNI.o
+g++ -c -I%JAVA_HOME%\include -I%JAVA_HOME%\include\win32 com_baeldung_jni_ExampleParametersJNI.cpp -o com_baeldung_jni_ExampleParametersJNI.o
+g++ -c -I%JAVA_HOME%\include -I%JAVA_HOME%\include\win32 com_baeldung_jni_ExampleObjectsJNI.cpp -o com_baeldung_jni_ExampleObjectsJNI.o
+g++ -shared -o ..\..\..\native\win32\native.dll com_baeldung_jni_HelloWorldJNI.o com_baeldung_jni_ExampleParametersJNI.o com_baeldung_jni_ExampleObjectsJNI.o -Wl,--add-stdcall-alias

core-java-modules/java-native/src/main/cpp/generateNativeLib.sh

@@ -0,0 +1,7 @@
+# Create the header with javac -h . ClassName.java
+# Remember to set your JAVA_HOME env var
+g++ -c -fPIC -I${JAVA_HOME}/include -I${JAVA_HOME}/include/linux com_baeldung_jni_HelloWorldJNI.cpp -o com_baeldung_jni_HelloWorldJNI.o
+g++ -c -fPIC -I${JAVA_HOME}/include -I${JAVA_HOME}/include/linux com_baeldung_jni_ExampleParametersJNI.cpp -o com_baeldung_jni_ExampleParametersJNI.o
+g++ -c -fPIC -I${JAVA_HOME}/include -I${JAVA_HOME}/include/linux com_baeldung_jni_ExampleObjectsJNI.cpp -o com_baeldung_jni_ExampleObjectsJNI.o
+g++ -shared -fPIC -o ../../../native/linux_x86_64/libnative.so com_baeldung_jni_HelloWorldJNI.o com_baeldung_jni_ExampleParametersJNI.o com_baeldung_jni_ExampleObjectsJNI.o -lc
+# Don't forget to set java.library.path to point to the folder where you have the libnative you're loading.

core-java-modules/java-native/src/main/cpp/generateNativeLibMac.sh

@@ -0,0 +1,7 @@
+# Create the header with javac -h . ClassName.java
+# Remember to set your JAVA_HOME env var
+g++ -c -fPIC -I${JAVA_HOME}/include -I${JAVA_HOME}/include/darwin com_baeldung_jni_HelloWorldJNI.cpp -o com_baeldung_jni_HelloWorldJNI.o
+g++ -c -fPIC -I${JAVA_HOME}/include -I${JAVA_HOME}/include/darwin com_baeldung_jni_ExampleParametersJNI.cpp -o com_baeldung_jni_ExampleParametersJNI.o
+g++ -c -fPIC -I${JAVA_HOME}/include -I${JAVA_HOME}/include/darwin com_baeldung_jni_ExampleObjectsJNI.cpp -o com_baeldung_jni_ExampleObjectsJNI.o
+g++ -c -fPIC -I${JAVA_HOME}/include -I${JAVA_HOME}/include/darwin com_baeldung_jni_RegisterNativesHelloWorldJNI.cpp -o com_baeldung_jni_RegisterNativesHelloWorldJNI.o
+g++ -dynamiclib -o ../../../native/macos/libnative.dylib com_baeldung_jni_HelloWorldJNI.o com_baeldung_jni_ExampleParametersJNI.o com_baeldung_jni_ExampleObjectsJNI.o com_baeldung_jni_RegisterNativesHelloWorldJNI.o -lc

core-java-modules/java-native/src/main/cpp/unsatisfiedlink/com_baeldung_unsatisfiedlink_JniUnsatisfiedLink.cpp

@@ -0,0 +1,13 @@
+#include "com_baeldung_unsatisfiedlink_JniUnsatisfiedLink.h"
+#include <iostream>
+
+/*
+ * Class:     com_baeldung_unsatisfiedlink_JniUnsatisfiedLink
+ * Method:    test
+ * Signature: ()Ljava/lang/String;
+ */
+JNIEXPORT jstring JNICALL Java_com_baeldung_unsatisfiedlink_JniUnsatisfiedLink_test (JNIEnv* env, jobject thisObject) {
+	std::string test = "Test OK";
+    std::cout << test << std::endl;
+    return env->NewStringUTF(test.c_str());
+}

core-java-modules/java-native/src/main/cpp/unsatisfiedlink/com_baeldung_unsatisfiedlink_JniUnsatisfiedLink.h

@@ -0,0 +1,21 @@
+/* DO NOT EDIT THIS FILE - it is machine generated */
+#include <jni.h>
+/* Header for class com_baeldung_unsatisfiedlink_JniUnsatisfiedLink */
+
+#ifndef _Included_com_baeldung_unsatisfiedlink_JniUnsatisfiedLink
+#define _Included_com_baeldung_unsatisfiedlink_JniUnsatisfiedLink
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*
+ * Class:     com_baeldung_unsatisfiedlink_JniUnsatisfiedLink
+ * Method:    test
+ * Signature: ()V
+ */
+JNIEXPORT jstring JNICALL Java_com_baeldung_unsatisfiedlink_JniUnsatisfiedLink_test
+  (JNIEnv *, jobject);
+
+#ifdef __cplusplus
+}
+#endif
+#endif

core-java-modules/java-native/src/main/cpp/unsatisfiedlink/generateNativeLib.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+# Create the header with javac -h . ClassName.java
+# Remember to set your JAVA_HOME env var
+# Don't forget to set java.library.path to point to the folder where you have the lib you're loading.
+MYSELF="$(readlink -f "$0")"
+MYDIR="${MYSELF%/*}"
+
+cd "$MYDIR"
+class_name=com_baeldung_unsatisfiedlink_JniUnsatisfiedLink
+lib_name=test
+
+g++ -c -fPIC -I"${JAVA_HOME}/include" -I"${JAVA_HOME}/include/linux" ${class_name}.cpp -o ${class_name}.o
+g++ -shared -fPIC -o lib${lib_name}.so ${class_name}.o -lc
+
+# 32-bit version
+g++ -m32 -c -fPIC -I"${JAVA_HOME}/include" -I"${JAVA_HOME}/include/linux" ${class_name}.cpp -o ${class_name}32.o
+g++ -m32 -shared -fPIC -o lib${lib_name}32.so ${class_name}32.o -lc
+
+# dummy version
+touch ${class_name}-dummy.o
+
+ls lib*

core-java-modules/java-native/src/main/java/com/baeldung/jna/CMath.java

@@ -0,0 +1,10 @@
+package com.baeldung.jna;
+
+import com.sun.jna.Library;
+import com.sun.jna.Native;
+import com.sun.jna.Platform;
+
+public interface CMath extends Library {
+    CMath INSTANCE = Native.load(Platform.isWindows() ? "msvcrt" : "c", CMath.class);
+    double cosh(double value);
+}

core-java-modules/java-native/src/main/java/com/baeldung/jna/Main.java

@@ -0,0 +1,8 @@
+package com.baeldung.jna;
+
+public class Main {
+	
+	public static void main(String[] args) {
+		
+	}
+}

core-java-modules/java-native/src/main/java/com/baeldung/jna/NativeFS.java

@@ -0,0 +1,46 @@
+package com.baeldung.jna;
+
+import java.util.Collections;
+import java.util.Map;
+
+import com.sun.jna.FunctionMapper;
+import com.sun.jna.LastErrorException;
+import com.sun.jna.Library;
+import com.sun.jna.Native;
+import com.sun.jna.NativeLong;
+import com.sun.jna.Platform;
+import com.sun.jna.Structure;
+import com.sun.jna.Structure.FieldOrder;
+
+public interface NativeFS extends Library {
+    
+    FunctionMapper mapper = (library,method) -> {
+        if (Platform.isWindows()) {
+            return "_" + method.getName();
+        }
+        else {
+            return "__x" + method.getName(); // On Linux, stat is actually _xstat
+        }
+    };
+    
+    public NativeFS INSTANCE = Native.load(Platform.isWindows() ? "msvcrt" : "c",
+      NativeFS.class,
+      Collections.singletonMap(Library.OPTION_FUNCTION_MAPPER, mapper));
+
+    int stat(String path, Stat stat) throws LastErrorException;
+
+    @FieldOrder({"st_dev","st_ino","st_mode","st_nlink","st_uid","st_gid","st_rdev","st_size","st_atime","st_mtime","st_ctime"})
+    public class Stat extends Structure {
+        public int st_dev;
+        public int st_ino;
+        public short st_mode;
+        public short st_nlink;
+        public short st_uid;
+        public short st_gid;
+        public int st_rdev;
+        public NativeLong st_size;
+        public NativeLong st_atime;
+        public NativeLong st_mtime;
+        public NativeLong st_ctime;
+    }
+}

core-java-modules/java-native/src/main/java/com/baeldung/jna/StdC.java

@@ -0,0 +1,17 @@
+package com.baeldung.jna;
+
+import com.sun.jna.LastErrorException;
+import com.sun.jna.Library;
+import com.sun.jna.Native;
+import com.sun.jna.Platform;
+import com.sun.jna.Pointer;
+
+public interface StdC extends Library {
+    StdC INSTANCE = Native.load(Platform.isWindows() ? "msvcrt" : "c", StdC.class );
+    Pointer malloc(long n);
+    void free(Pointer p);
+    Pointer memset(Pointer p, int c, long n);
+    int open(String path, int flags) throws LastErrorException;
+    int close(int fd) throws LastErrorException;
+}
+

core-java-modules/java-native/src/main/java/com/baeldung/jni/ExampleObjectsJNI.java

@@ -0,0 +1,19 @@
+package com.baeldung.jni;
+
+public class ExampleObjectsJNI {
+
+    static {
+        System.loadLibrary("native");
+    }
+    
+    public static void main(String[] args) {
+        ExampleObjectsJNI instance = new ExampleObjectsJNI();
+        UserData newUser = instance.createUser("John Doe", 450.67);
+        instance.printUserData(newUser);
+    }
+    
+    public native UserData createUser(String name, double balance);
+    
+    public native String printUserData(UserData user);
+
+}

core-java-modules/java-native/src/main/java/com/baeldung/jni/ExampleParametersJNI.java

@@ -0,0 +1,20 @@
+package com.baeldung.jni;
+
+public class ExampleParametersJNI {
+
+    static {
+        System.loadLibrary("native");
+    }
+    
+    public static void main(String[] args) {  
+        System.out.println("Java: My full name: " + new ExampleParametersJNI().sayHelloToMe("Martin", false));
+        long sumFromNative = new ExampleParametersJNI().sumIntegers(456, 44);
+        System.out.println("Java: The sum coming from native code is: " + sumFromNative);
+    }
+    
+    // Declare another method sumIntegers that receives two integers and return a long with the sum
+    public native long sumIntegers(int first, int second);
+    
+    // Declare another method sayHelloToMe that receives the name and gender and returns the proper salutation
+    public native String sayHelloToMe(String name, boolean isFemale);
+}

core-java-modules/java-native/src/main/java/com/baeldung/jni/HelloWorldJNI.java

@@ -0,0 +1,15 @@
+package com.baeldung.jni;
+
+public class HelloWorldJNI {
+
+    static {
+        System.loadLibrary("native");
+    }
+    
+    public static void main(String[] args) {
+        new HelloWorldJNI().sayHello();
+    }
+
+    // Declare a native method sayHello() that receives no arguments and returns void
+    public native String sayHello();
+}

core-java-modules/java-native/src/main/java/com/baeldung/jni/RegisterNativesHelloWorldJNI.java

@@ -0,0 +1,18 @@
+package com.baeldung.jni;
+
+public class RegisterNativesHelloWorldJNI {
+
+    static {
+        System.loadLibrary("native");
+    }
+
+    public static void main(String[] args) {
+        RegisterNativesHelloWorldJNI helloWorldJNI = new RegisterNativesHelloWorldJNI();
+        helloWorldJNI.register();
+        helloWorldJNI.sayHello();
+    }
+
+    public native String sayHello();
+
+    public native void register();
+}

core-java-modules/java-native/src/main/java/com/baeldung/jni/UserData.java

@@ -0,0 +1,11 @@
+package com.baeldung.jni;
+
+public class UserData {
+    
+    public String name;
+    public double balance;
+    
+    public String getUserInfo() {
+        return "[name]=" + name + ", [balance]=" + balance;
+    }
+}

core-java-modules/java-native/src/main/java/com/baeldung/jvmbitversion/JVMBitVersion.java

@@ -0,0 +1,24 @@
+package com.baeldung.jvmbitversion;
+
+import com.sun.jna.Platform;
+
+public class JVMBitVersion {
+
+    public String getUsingSystemClass() {
+        return System.getProperty("sun.arch.data.model") + "-bit";
+    }
+
+    public String getUsingNativeClass() {
+        if (com.sun.jna.Native.POINTER_SIZE == 8) {
+            return "64-bit";
+        } else if (com.sun.jna.Native.POINTER_SIZE == 4) {
+            return "32-bit";
+        } else
+            return "unknown";
+    }
+
+    public boolean getUsingPlatformClass() {
+        return (Platform.is64Bit());
+    }
+
+}

core-java-modules/java-native/src/main/java/com/baeldung/unsatisfiedlink/JniUnsatisfiedLink.java

@@ -0,0 +1,15 @@
+package com.baeldung.unsatisfiedlink;
+
+public class JniUnsatisfiedLink {
+
+    public static final String LIB_NAME = "test";
+
+    public static void main(String[] args) {
+        System.loadLibrary(LIB_NAME);
+        new JniUnsatisfiedLink().test();
+    }
+
+    public native String test();
+
+    public native String nonexistentDllMethod();
+}

core-java-modules/java-native/src/main/resources/logback.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

core-java-modules/java-native/src/main/resources/unsatisfiedlink/jni.policy

@@ -0,0 +1,3 @@
+grant {
+    permission java.lang.RuntimePermission "loadLibrary.test";
+};

core-java-modules/java-native/src/test/java/com/baeldung/jna/CMathUnitTest.java

@@ -0,0 +1,18 @@
+package com.baeldung.jna;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+import com.sun.jna.Native;
+import com.sun.jna.Platform;
+
+class CMathUnitTest {
+    @Test
+    void whenCallNative_thenSuccess() {
+        CMath lib = Native.load(Platform.isWindows() ? "msvcrt" : "c", CMath.class);
+        double result = lib.cosh(0);
+        assertEquals(1.0,result);
+    }
+
+}

core-java-modules/java-native/src/test/java/com/baeldung/jna/NativeFSUnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.jna;
+
+import static org.junit.Assert.fail;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+
+import org.junit.jupiter.api.Test;
+
+import com.baeldung.jna.NativeFS.Stat;
+import com.sun.jna.LastErrorException;
+import com.sun.jna.Platform;
+
+public class NativeFSUnitTest {
+    
+
+    @Test
+    public void whenCallNative_thenSuccess() throws IOException {
+        NativeFS lib = NativeFS.INSTANCE;
+        
+        File f = Files.createTempFile("junit", ".bin").toFile(); 
+        f.deleteOnExit();
+        Stat stat = new Stat();
+        try {
+            if (Platform.isWindows()) {
+                int rc = lib.stat(f.getAbsolutePath(), stat);
+                assertEquals(0, rc);
+                assertEquals(0,stat.st_size.longValue());
+            }
+        }
+        catch(LastErrorException error) {
+            fail("stat failed: error code=" + error.getErrorCode());
+        }
+        
+    }
+}

core-java-modules/java-native/src/test/java/com/baeldung/jna/StdCUnitTest.java

@@ -0,0 +1,47 @@
+package com.baeldung.jna;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.BeforeClass;
+import org.junit.jupiter.api.Test;
+
+import com.sun.jna.Native;
+import com.sun.jna.Platform;
+import com.sun.jna.Pointer;
+
+class StdCUnitTest {
+    
+    @BeforeClass
+    public static void setupProtectedMode() {
+        Native.setProtected(true);
+    }
+
+    @Test
+    public void whenMalloc_thenSuccess() {
+        StdC lib = StdC.INSTANCE;
+        Pointer p = lib.malloc(1024);
+        p.setMemory(0l, 1024l, (byte) 0);
+        lib.free(p);
+    }
+    
+    @Test
+    public void whenAccessViolation_thenShouldThrowError() {
+        // Running this test on Linux requires additional setup using libjsig.so
+        // Details here: http://java-native-access.github.io/jna/5.6.0/javadoc/overview-summary.html#crash-protection
+        // IMPORTANT NOTICE: Code for illustration purposes only. DON'T DO THIS IN YOUR OWN CODE
+        if ( Platform.isWindows()) {
+            Error e = null;
+            Pointer p = new Pointer(0l);
+            
+            try {
+                p.setMemory(0, 100*1024, (byte) 0);
+            }
+            catch(Error err) {
+                e = err;
+            }
+            
+            assertNotNull(e, "Should throw Error");
+        }
+    }
+
+}

core-java-modules/java-native/src/test/java/com/baeldung/jni/JNINativeManualTest.java

@@ -0,0 +1,58 @@
+package com.baeldung.jni;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class JNINativeManualTest {
+    
+    @Before
+    public void setup() {
+        System.loadLibrary("native");
+    }
+    
+    @Test
+    public void whenNativeHelloWorld_thenOutputIsAsExpected() {
+        HelloWorldJNI helloWorld = new HelloWorldJNI();
+        String helloFromNative = helloWorld.sayHello();
+        assertTrue(!helloFromNative.isEmpty() && helloFromNative.equals("Hello from C++ !!"));
+    }
+    
+    @Test
+    public void whenSumNative_thenResultIsArithmeticallyCorrect() {
+        ExampleParametersJNI parametersNativeMethods = new ExampleParametersJNI();
+        assertTrue(parametersNativeMethods.sumIntegers(200, 400) == 600L);
+    }
+    
+    @Test
+    public void whenSayingNativeHelloToMe_thenResultIsAsExpected() {
+        ExampleParametersJNI parametersNativeMethods = new ExampleParametersJNI();
+        assertEquals(parametersNativeMethods.sayHelloToMe("Orange", true), "Ms. Orange");
+    }
+
+    @Test
+    public void whenCreatingNativeObject_thenObjectIsNotNullAndHasCorrectData() {
+        String name = "Iker Casillas";
+        double balance = 2378.78;
+        ExampleObjectsJNI objectsNativeMethods = new ExampleObjectsJNI();
+        UserData userFromNative = objectsNativeMethods.createUser(name, balance);
+        assertNotNull(userFromNative);
+        assertEquals(userFromNative.name, name);
+        assertTrue(userFromNative.balance == balance);
+    }
+    
+    @Test
+    public void whenNativeCallingObjectMethod_thenResultIsAsExpected() {
+        String name = "Sergio Ramos";
+        double balance = 666.77;
+        ExampleObjectsJNI objectsNativeMethods = new ExampleObjectsJNI();
+        UserData userData = new UserData();
+        userData.name = name;
+        userData.balance = balance;
+        assertEquals(objectsNativeMethods.printUserData(userData), "[name]=" + name + ", [balance]=" + balance);
+    }
+    
+}

core-java-modules/java-native/src/test/java/com/baeldung/jni/registernatives/JNIRegisterNativesManualTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.jni.registernatives;
+
+import com.baeldung.jni.RegisterNativesHelloWorldJNI;
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+public class JNIRegisterNativesManualTest {
+    @Before
+    public void setup() {
+        System.loadLibrary("native");
+    }
+
+    @Test
+    public void whenRegisteredNativeHelloWorld_thenOutputIsAsExpected() {
+        RegisterNativesHelloWorldJNI helloWorld = new RegisterNativesHelloWorldJNI();
+        helloWorld.register();
+
+        String helloFromNative = helloWorld.sayHello();
+
+        assertNotNull(helloFromNative);
+        assertTrue(helloFromNative.equals("Hello from registered native C++ !!"));
+    }
+}

core-java-modules/java-native/src/test/java/com/baeldung/jvmbitversion/JVMBitVersionUnitTest.java

@@ -0,0 +1,45 @@
+package com.baeldung.jvmbitversion;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import com.sun.jna.Platform;
+
+public class JVMBitVersionUnitTest {
+
+    private JVMBitVersion jvmVersion;
+
+    @Before
+    public void setup() {
+        jvmVersion = new JVMBitVersion();
+    }
+
+    @Test
+    public void whenUsingSystemClass_thenOutputIsAsExpected() {
+        if ("64".equals(System.getProperty("sun.arch.data.model"))) {
+            assertEquals("64-bit", jvmVersion.getUsingSystemClass());
+        } else if ("32".equals(System.getProperty("sun.arch.data.model"))) {
+            assertEquals("32-bit", jvmVersion.getUsingSystemClass());
+        }
+    }
+    
+    @Test
+    public void whenUsingNativeClass_thenResultIsAsExpected() {
+        if (com.sun.jna.Native.POINTER_SIZE == 8) {
+            assertEquals("64-bit", jvmVersion.getUsingNativeClass());
+        } else if (com.sun.jna.Native.POINTER_SIZE == 4) {
+            assertEquals("32-bit", jvmVersion.getUsingNativeClass());
+        }
+    }
+
+    @Test
+    public void whenUsingPlatformClass_thenResultIsAsExpected() {
+        if (Platform.is64Bit() == Boolean.TRUE) {
+            assertEquals(Boolean.TRUE, jvmVersion.getUsingPlatformClass());
+        } else if (com.sun.jna.Native.POINTER_SIZE == 4) {
+            assertEquals(Boolean.FALSE, jvmVersion.getUsingPlatformClass());
+        }
+    }
+}

core-java-modules/java-native/src/test/java/com/baeldung/unsatisfiedlink/JniUnsatisfiedLinkManualTest.java

@@ -0,0 +1,105 @@
+package com.baeldung.unsatisfiedlink;
+
+import static com.baeldung.unsatisfiedlink.JniUnsatisfiedLink.LIB_NAME;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.File;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+public class JniUnsatisfiedLinkManualTest {
+
+    static String osLibPrefix = "";
+    static String osLibSuffix = "";
+
+    @BeforeAll
+    static void setup() {
+        String osName = System.getProperty("os.name")
+            .toLowerCase();
+
+        if (osName.contains("win")) {
+            osLibSuffix = ".dll";
+        } else if (osName.contains("nix") || osName.contains("nux") || osName.contains("mac")) {
+            osLibPrefix = "lib";
+            osLibSuffix = ".so";
+            if (osName.contains("mac")) {
+                osLibPrefix = "lib";
+                osLibSuffix = ".dylib";
+            }
+        } else {
+            throw new UnsupportedOperationException("Unsupported operating system: " + osName);
+        }
+    }
+
+    @Test
+    public void whenCorrectLibName_thenLibLoaded() {
+        assertDoesNotThrow(() -> {
+            System.loadLibrary(LIB_NAME);
+            new JniUnsatisfiedLink().test();
+        });
+    }
+
+    @Test
+    public void whenIncorrectLibName_thenLibNotFound() {
+        String libName = osLibPrefix + LIB_NAME + osLibSuffix;
+
+        Error error = assertThrows(UnsatisfiedLinkError.class, () -> System.loadLibrary(libName));
+
+        assertEquals(String.format("no %s in java.library.path", libName), error.getMessage());
+    }
+
+    @Test
+    public void whenLoadLibraryContainsPathSeparator_thenErrorThrown() {
+        String libName = "/" + LIB_NAME;
+
+        Error error = assertThrows(UnsatisfiedLinkError.class, () -> System.loadLibrary(libName));
+
+        assertEquals(String.format("Directory separator should not appear in library name: %s", libName), error.getMessage());
+    }
+
+    @Test
+    public void whenLoadWithoutAbsolutePath_thenErrorThrown() {
+        String libName = LIB_NAME;
+
+        Error error = assertThrows(UnsatisfiedLinkError.class, () -> System.load(libName));
+
+        assertEquals(String.format("Expecting an absolute path of the library: %s", libName), error.getMessage());
+    }
+
+    @Test
+    public void whenUnlinkedMethod_thenErrorThrown() {
+        System.loadLibrary(LIB_NAME);
+
+        Error error = assertThrows(UnsatisfiedLinkError.class, () -> new JniUnsatisfiedLink().nonexistentDllMethod());
+
+        assertTrue(error.getMessage()
+            .contains("JniUnsatisfiedLink.nonexistentDllMethod"));
+    }
+
+    @Test
+    public void whenIncompatibleArchitecture_thenErrorThrown() {
+        Error error = assertThrows(UnsatisfiedLinkError.class, () -> System.loadLibrary(LIB_NAME + "32"));
+
+        assertTrue(error.getMessage()
+            .contains("wrong ELF class: ELFCLASS32"));
+    }
+
+    @Test
+    public void whenCorruptedFile_thenErrorThrown() {
+        String libPath = System.getProperty("java.library.path");
+        assertNotNull(libPath);
+
+        String dummyLib = LIB_NAME + "-dummy";
+        assertTrue(new File(libPath, osLibPrefix + dummyLib + osLibSuffix).isFile());
+
+        Error error = assertThrows(UnsatisfiedLinkError.class, () -> System.loadLibrary(dummyLib));
+
+        assertTrue(error.getMessage()
+            .contains("file too short"));
+    }
+}

core-java-modules/pom.xml

@@ -199,6 +199,7 @@
         <module>core-java-date-operations-1</module>
         <!--<module>core-java-datetime-conversion</module>--> <!--JAVA-25433-->
         <module>core-java-httpclient</module>
+        <module>java-native</module>
     </modules>
 
     <dependencyManagement>