Merge remote-tracking branch 'upstream/master' into feature/BAEL-6695-BooleanValidation

.github/ISSUE_TEMPLATE/issue_report.md

@@ -5,7 +5,7 @@ title: '[ISSUE] '
 ---
 
 **Article and Module Links**
-A link to the affected article and the affected module. The link to the module is the one in the "over on GitHub" standard phrase.
+A link to the affected article and the affected module. You can find the link to the module in the Conclusion section in the "on Github" standard phase.
 
 **Describe the Issue**
 A clear and concise description of what the issue is.
@@ -30,9 +30,3 @@ If applicable, add screenshots to help explain your problem.
 
 **Additional Context**
 Add any other context about the issue here.
-
-Note that, unfortunately, we can only help with issues that are specifically and directly related to the article - not with your own, custom application.
-
-StackOverflow is a great place to ask more general questions.
-
-That's primarily because we get a large number of questions and - while we do try to go through as much as everything and help wherever we can, we can't really get back to all of them.

apache-poi-3/README.md

@@ -0,0 +1,3 @@
+## Relevant Articles
+- [How To Convert Excel Data Into List Of Java Objects](https://www.baeldung.com/java-convert-excel-data-into-list)
+- [Expand Columns with Apache POI](https://www.baeldung.com/java-apache-poi-expand-columns)

core-java-modules/core-java-16/README.md

@@ -5,3 +5,4 @@
 - [Collecting Stream Elements into a List in Java](https://www.baeldung.com/java-stream-to-list-collecting)
 - [New Features in Java 16](https://www.baeldung.com/java-16-new-features)
 - [Guide to Java 8 groupingBy Collector](https://www.baeldung.com/java-groupingby-collector)
+- [Value-Based Classes in Java](https://www.baeldung.com/java-value-based-classes)

core-java-modules/core-java-21/README.md

@@ -1,2 +1,3 @@
 ## Relevant Articles
 - [Sequenced Collections in Java 21](https://www.baeldung.com/java-21-sequenced-collections)
+- [String Templates in Java 21](https://www.baeldung.com/java-21-string-templates)

core-java-modules/core-java-21/pom.xml

@@ -12,6 +12,12 @@
         <version>0.0.1-SNAPSHOT</version>
     </parent>
 
+    <properties>
+        <maven.compiler.source.version>21</maven.compiler.source.version>
+        <maven.compiler.target.version>21</maven.compiler.target.version>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
     <build>
         <plugins>
             <plugin>
@@ -20,14 +26,22 @@
                 <configuration>
                     <source>21</source>
                     <target>21</target>
-                    <compilerArgs>--enable-preview</compilerArgs>
+                    <!-- Needed due to a bug with JDK 21, described here: https://issues.apache.org/jira/browse/MCOMPILER-546?page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel&focusedCommentId=17767513 -->
+                    <debug>false</debug>
+                    <compilerArgs>
+                        <arg>--enable-preview</arg>
+                    </compilerArgs>
                 </configuration>
             </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <configuration>
+                    <argLine>--enable-preview</argLine>
+                </configuration>
+            </plugin>
+
         </plugins>
     </build>
-    <properties>
-        <maven.compiler.source.version>21</maven.compiler.source.version>
-        <maven.compiler.target.version>21</maven.compiler.target.version>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-    </properties>
+
 </project>

core-java-modules/core-java-21/src/main/java/com/baeldung/unnamed/variables/Car.java

@@ -0,0 +1,11 @@
+package com.baeldung.unnamed.variables;
+
+public record Car<T extends Engine>(String name, String color, T engine) { }
+
+abstract class Engine { }
+
+class GasEngine extends Engine { }
+
+class ElectricEngine extends Engine { }
+
+class HybridEngine extends Engine { }

core-java-modules/core-java-21/src/main/java/com/baeldung/unnamed/variables/UnnamedPatterns.java

@@ -0,0 +1,50 @@
+package com.baeldung.unnamed.variables;
+
+public class UnnamedPatterns {
+
+    static String getObjectsColorWithNamedPattern(Object object) {
+        if (object instanceof Car(String name, String color, Engine engine)) {
+            return color;
+        }
+        return "No color!";
+    }
+
+    static String getObjectsColorWithUnnamedPattern(Object object) {
+        if (object instanceof Car(_, String color, _)) {
+            return color;
+        }
+        return "No color!";
+    }
+
+    static String getObjectsColorWithSwitchAndNamedPattern(Object object) {
+        return switch (object) {
+            case Car(String name, String color, Engine engine) -> color;
+            default -> "No color!";
+        };
+    }
+
+    static String getObjectsColorWithSwitchAndUnnamedPattern(Object object) {
+        return switch (object) {
+            case Car(_, String color, _) -> color;
+            default -> "No color!";
+        };
+    }
+
+    static String getEngineTypeWithNamedPattern(Car<?> car) {
+        return switch (car) {
+            case Car(String name, String color, GasEngine engine) -> "gas";
+            case Car(String name, String color, ElectricEngine engine) -> "electric";
+            case Car(String name, String color, HybridEngine engine) -> "hybrid";
+            default -> "none";
+        };
+    }
+
+    static String getEngineTypeWithUnnamedPattern(Car<?> car) {
+        return switch (car) {
+            case Car(_, _, GasEngine _) -> "gas";
+            case Car(_, _, ElectricEngine _) -> "electric";
+            case Car(_, _, HybridEngine _) -> "hybrid";
+            default -> "none";
+        };
+    }
+}

core-java-modules/core-java-21/src/main/java/com/baeldung/unnamed/variables/UnnamedVariables.java

@@ -0,0 +1,134 @@
+package com.baeldung.unnamed.variables;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Queue;
+
+class Transaction implements AutoCloseable {
+
+    @Override
+    public void close() {
+        System.out.println("Closed!");
+    }
+}
+
+public class UnnamedVariables {
+
+    static int countCarsOverLimitWithNamedVariable(Collection<Car<?>> cars, int limit) {
+        var total = 0;
+        var totalOverLimit = 0;
+        for (var car : cars) {
+            total++;
+            if (total > limit) {
+                totalOverLimit++;
+                // side effect
+            }
+        }
+        return totalOverLimit;
+    }
+
+    static int countCarsOverLimitWithUnnamedVariable(Collection<Car<?>> cars, int limit) {
+        var total = 0;
+        var totalOverLimit = 0;
+        for (var _ : cars) {
+            total++;
+            if (total > limit) {
+                totalOverLimit++;
+                // side effect
+            }
+        }
+        return totalOverLimit;
+    }
+
+    static void sendNotificationToCarsWithNamedVariable(Collection<Car<?>> cars) {
+        sendOneTimeNotification();
+        for (int i = 0; i < cars.size(); i++) {
+            // Notify car
+        }
+    }
+
+    static void sendNotificationToCarsWithUnnamedVariable(Collection<Car<?>> cars) {
+        for (int i = 0, _ = sendOneTimeNotification(); i < cars.size(); i++) {
+            // Notify car
+        }
+    }
+
+    private static int sendOneTimeNotification() {
+        System.out.println("Sending one time notification!");
+        return 1;
+    }
+
+    static Car<?> removeThreeCarsAndReturnFirstRemovedWithNamedVariables(Queue<Car<?>> cars) {
+        var x = cars.poll();
+        var y = cars.poll();
+        var z = cars.poll();
+        return x;
+    }
+
+    static Car<?> removeThreeCarsAndReturnFirstRemovedWithUnnamedVariables(Queue<Car<?>> cars) {
+        var car = cars.poll();
+        var _ = cars.poll();
+        var _ = cars.poll();
+        return car;
+    }
+
+    static void handleCarExceptionWithNamedVariables(Car<?> car) {
+        try {
+            someOperationThatFails(car);
+        } catch (IllegalStateException ex) {
+            System.out.println("Got an illegal state exception for: " + car.name());
+        } catch (RuntimeException ex) {
+            System.out.println("Got a runtime exception!");
+        }
+    }
+
+    static void handleCarExceptionWithUnnamedVariables(Car<?> car) {
+        try {
+            someOperationThatFails(car);
+        } catch (IllegalStateException | NumberFormatException _) {
+            System.out.println("Got an illegal state exception for: " + car.name());
+        } catch (RuntimeException _) {
+            System.out.println("Got a runtime exception!");
+        }
+    }
+
+    static void obtainTransactionAndUpdateCarWithNamedVariables(Car<?> car) {
+        try (var transaction = new Transaction()) {
+            updateCar(car);
+        }
+    }
+
+    static void obtainTransactionAndUpdateCarWithUnnamedVariables(Car<?> car) {
+        try (var _ = new Transaction()) {
+            updateCar(car);
+        }
+    }
+
+    static void updateCar(Car<?> car) {
+        // Some update logic
+        System.out.println("Car updated!");
+    }
+
+    static Map<String, List<Car<?>>> getCarsByFirstLetterWithNamedVariables(List<Car<?>> cars) {
+        Map<String, List<Car<?>>> carMap = new HashMap<>();
+        cars.forEach(car ->
+            carMap.computeIfAbsent(car.name().substring(0, 1), firstLetter -> new ArrayList<>()).add(car)
+        );
+        return carMap;
+    }
+
+    static Map<String, List<Car<?>>> getCarsByFirstLetterWithUnnamedVariables(List<Car<?>> cars) {
+        Map<String, List<Car<?>>> carMap = new HashMap<>();
+        cars.forEach(car ->
+            carMap.computeIfAbsent(car.name().substring(0, 1), _ -> new ArrayList<>()).add(car)
+        );
+        return carMap;
+    }
+
+    private static void someOperationThatFails(Car<?> car) {
+        throw new IllegalStateException("Triggered exception for: " + car.name());
+    }
+}

core-java-modules/core-java-21/src/main/java/com/baeldung/unnamedclasses/HelloWorld.java

@@ -0,0 +1,3 @@
+void main() {
+    System.out.println("Hello, World!");
+}

core-java-modules/core-java-21/src/main/java/com/baeldung/unnamedclasses/HelloWorldChild.java

@@ -0,0 +1,7 @@
+package com.baeldung.unnamedclasses;
+
+public class HelloWorldChild extends HelloWorldSuper {
+    void main() {
+        System.out.println("Hello, World!");
+    }
+}

core-java-modules/core-java-21/src/main/java/com/baeldung/unnamedclasses/HelloWorldSuper.java

@@ -0,0 +1,7 @@
+package com.baeldung.unnamedclasses;
+
+public class HelloWorldSuper {
+    public static void main(String[] args) {
+        System.out.println("Hello from the superclass");
+    }
+}

core-java-modules/core-java-21/src/main/java/com/baeldung/unnamedclasses/HelloWorldWithMethod.java

@@ -0,0 +1,6 @@
+private String getMessage() {
+    return "Hello, World!";
+}
+void main() {
+    System.out.println(getMessage());
+}

core-java-modules/core-java-21/src/test/java/com/baeldung/unnamed/variables/CarScenario.java

@@ -0,0 +1,13 @@
+package com.baeldung.unnamed.variables;
+
+import java.util.List;
+
+class CarScenario {
+
+    protected final List<Car<?>> cars = List.of(
+        new Car<>("Mitsubishi", "blue", new GasEngine()),
+        new Car<>("Toyota", "red", new ElectricEngine()),
+        new Car<>("Jaguar", "white", new HybridEngine())
+    );
+
+}

core-java-modules/core-java-21/src/test/java/com/baeldung/unnamed/variables/UnnamedPatternsUnitTest.java

@@ -0,0 +1,44 @@
+package com.baeldung.unnamed.variables;
+
+import static com.baeldung.unnamed.variables.UnnamedPatterns.getEngineTypeWithNamedPattern;
+import static com.baeldung.unnamed.variables.UnnamedPatterns.getEngineTypeWithUnnamedPattern;
+import static com.baeldung.unnamed.variables.UnnamedPatterns.getObjectsColorWithNamedPattern;
+import static com.baeldung.unnamed.variables.UnnamedPatterns.getObjectsColorWithSwitchAndNamedPattern;
+import static com.baeldung.unnamed.variables.UnnamedPatterns.getObjectsColorWithSwitchAndUnnamedPattern;
+import static com.baeldung.unnamed.variables.UnnamedPatterns.getObjectsColorWithUnnamedPattern;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class UnnamedPatternsUnitTest extends CarScenario {
+
+    @Test
+    public void whenExtractingColorWithNamedPatterns_thenReturnBlue() {
+        assertEquals("blue", getObjectsColorWithNamedPattern(cars.get(0)));
+    }
+
+    @Test
+    public void whenExtractingColorWithUnnamedPatterns_thenReturnBlue() {
+        assertEquals("blue", getObjectsColorWithUnnamedPattern(cars.get(0)));
+    }
+
+    @Test
+    public void whenExtractingColorWithSwitchAndNamedPatterns_thenReturnBlue() {
+        assertEquals("blue", getObjectsColorWithSwitchAndNamedPattern(cars.get(0)));
+    }
+
+    @Test
+    public void whenExtractingColorWithSwitchAndUnnamedPatterns_thenReturnBlue() {
+        assertEquals("blue", getObjectsColorWithSwitchAndUnnamedPattern(cars.get(0)));
+    }
+
+    @Test
+    public void whenExtractingEngineTypeWithNamedPatterns_thenReturnGas() {
+        assertEquals("gas", getEngineTypeWithNamedPattern(cars.get(0)));
+    }
+
+    @Test
+    public void whenExtractingEngineTypeWithUnnamedPatterns_thenReturnGas() {
+        assertEquals("gas", getEngineTypeWithUnnamedPattern(cars.get(0)));
+    }
+}

core-java-modules/core-java-21/src/test/java/com/baeldung/unnamed/variables/UnnamedVariablesUnitTest.java

@@ -0,0 +1,93 @@
+package com.baeldung.unnamed.variables;
+
+import static com.baeldung.unnamed.variables.UnnamedVariables.countCarsOverLimitWithNamedVariable;
+import static com.baeldung.unnamed.variables.UnnamedVariables.countCarsOverLimitWithUnnamedVariable;
+import static com.baeldung.unnamed.variables.UnnamedVariables.getCarsByFirstLetterWithNamedVariables;
+import static com.baeldung.unnamed.variables.UnnamedVariables.getCarsByFirstLetterWithUnnamedVariables;
+import static com.baeldung.unnamed.variables.UnnamedVariables.handleCarExceptionWithNamedVariables;
+import static com.baeldung.unnamed.variables.UnnamedVariables.handleCarExceptionWithUnnamedVariables;
+import static com.baeldung.unnamed.variables.UnnamedVariables.obtainTransactionAndUpdateCarWithNamedVariables;
+import static com.baeldung.unnamed.variables.UnnamedVariables.obtainTransactionAndUpdateCarWithUnnamedVariables;
+import static com.baeldung.unnamed.variables.UnnamedVariables.removeThreeCarsAndReturnFirstRemovedWithNamedVariables;
+import static com.baeldung.unnamed.variables.UnnamedVariables.removeThreeCarsAndReturnFirstRemovedWithUnnamedVariables;
+import static com.baeldung.unnamed.variables.UnnamedVariables.sendNotificationToCarsWithNamedVariable;
+import static com.baeldung.unnamed.variables.UnnamedVariables.sendNotificationToCarsWithUnnamedVariable;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.LinkedList;
+
+import org.junit.jupiter.api.Test;
+
+public class UnnamedVariablesUnitTest extends CarScenario {
+
+    @Test
+    public void whenCountingCarsOverLimitWithNamedVariables_thenShouldReturnOne() {
+        assertEquals(1, countCarsOverLimitWithNamedVariable(cars, 2));
+    }
+
+    @Test
+    public void whenCountingCarsOverLimitWithUnnamedVariables_thenShouldReturnOne() {
+        assertEquals(1, countCarsOverLimitWithUnnamedVariable(cars, 2));
+    }
+
+    @Test
+    public void whenNotifyingCarsWithNamedVariables_thenShouldNotFail() {
+        assertDoesNotThrow(() -> sendNotificationToCarsWithNamedVariable(cars));
+    }
+
+    @Test
+    public void whenNotifyingCarsWithUnnamedVariables_thenShouldNotFail() {
+        assertDoesNotThrow(() -> sendNotificationToCarsWithUnnamedVariable(cars));
+    }
+
+    @Test
+    public void whenPollingCarsWithNamedVariables_thenReturnFirstOneAndEmptyQueue() {
+        var carQueue = new LinkedList<>(cars);
+        assertEquals("Mitsubishi", removeThreeCarsAndReturnFirstRemovedWithNamedVariables(carQueue).name());
+        assertEquals(0, carQueue.size());
+    }
+
+    @Test
+    public void whenPollingCarsWithUnnamedVariables_thenReturnFirstOneAndEmptyQueue() {
+        var carQueue = new LinkedList<>(cars);
+        assertEquals("Mitsubishi", removeThreeCarsAndReturnFirstRemovedWithUnnamedVariables(carQueue).name());
+        assertEquals(0, carQueue.size());
+    }
+
+    @Test
+    public void whenHandlingExceptionWithNamedVariables_thenNoExceptionIsThrown() {
+        assertDoesNotThrow(() -> handleCarExceptionWithNamedVariables(cars.get(0)));
+    }
+
+    @Test
+    public void whenHandlingExceptionWithUnnamedVariables_thenNoExceptionIsThrown() {
+        assertDoesNotThrow(() -> handleCarExceptionWithUnnamedVariables(cars.get(0)));
+    }
+
+    @Test
+    public void whenHandlingTransactionUpdateWithNamedVariables_thenNoExceptionIsThrown() {
+        assertDoesNotThrow(() -> obtainTransactionAndUpdateCarWithNamedVariables(cars.get(0)));
+    }
+
+    @Test
+    public void whenHandlingTransactionUpdateWithUnnamedVariables_thenNoExceptionIsThrown() {
+        assertDoesNotThrow(() -> obtainTransactionAndUpdateCarWithUnnamedVariables(cars.get(0)));
+    }
+
+    @Test
+    public void whenGettingCarsByFirstLetterWithNamedVariables_thenHaveThreeKeys() {
+        var carsByLetter = getCarsByFirstLetterWithNamedVariables(cars);
+        assertEquals(1, carsByLetter.get("M").size());
+        assertEquals(1, carsByLetter.get("T").size());
+        assertEquals(1, carsByLetter.get("J").size());
+    }
+
+    @Test
+    public void whenGettingCarsByFirstLetterWithUnnamedVariables_thenHaveThreeKeys() {
+        var carsByLetter = getCarsByFirstLetterWithUnnamedVariables(cars);
+        assertEquals(1, carsByLetter.get("M").size());
+        assertEquals(1, carsByLetter.get("T").size());
+        assertEquals(1, carsByLetter.get("J").size());
+    }
+}

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

@@ -4,3 +4,4 @@ This module contains articles about Java 9 streams
 
 ### Relevant Articles: 
 - [How to Break from Java Stream forEach](https://www.baeldung.com/java-break-stream-foreach)
+- [Creating Stream of Regex Matches](https://www.baeldung.com/java-stream-regex-matches)

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

@@ -9,3 +9,4 @@ This module contains complete guides about arrays in Java
 - [Guide to ArrayStoreException](https://www.baeldung.com/java-arraystoreexception)
 - [Creating a Generic Array in Java](https://www.baeldung.com/java-generic-array)
 - [Maximum Size of Java Arrays](https://www.baeldung.com/java-arrays-max-size)
+- [Merge Two Arrays and Remove Duplicates in Java](https://www.baeldung.com/java-merge-two-arrays-delete-duplicates)

core-java-modules/core-java-arrays-operations-advanced-2/README.md

@@ -0,0 +1,2 @@
+## Relevant Articles
+- [Find the Middle Element of an Array in Java](https://www.baeldung.com/java-array-middle-item)

core-java-modules/core-java-arrays-operations-advanced/README.md

@@ -14,4 +14,3 @@ This module contains articles about advanced operations on arrays in Java. They
 - [Slicing Arrays in Java](https://www.baeldung.com/java-slicing-arrays)
 - [Combining Two or More Byte Arrays](https://www.baeldung.com/java-concatenate-byte-arrays)
 - [Calculating the Sum of Two Arrays in Java](https://www.baeldung.com/java-sum-arrays-element-wise)
-- [Find the Middle Element of an Array in Java](https://www.baeldung.com/java-array-middle-item)

core-java-modules/core-java-char/src/test/java/com/baeldung/incrementchar/IncrementCharUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.incrementchar;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+class IncrementCharUnitTest {
+    @Test
+    void whenUsingForLoop_thenGenerateCharacters(){
+        final List<Character> allCapitalCharacters = Arrays.asList('A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z');
+        List<Character> characters = new ArrayList<>();
+        for (char character = 'A'; character <= 'Z'; character++) {
+            characters.add(character);
+        }
+        Assertions.assertEquals(characters, allCapitalCharacters);
+    }
+
+    @Test
+    void whenUsingStreams_thenGenerateCharacters() {
+        final List<Character> allCapitalCharacters = Arrays.asList('A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z');
+        final List<Character> characters = IntStream.rangeClosed('A', 'Z').mapToObj(c -> (char) c).collect(Collectors.toList());
+        Assertions.assertEquals(characters, allCapitalCharacters);
+    }
+}

core-java-modules/core-java-collections-5/src/main/java/com/baeldung/skippingfirstelement/SkipFirstElementExample.java

@@ -0,0 +1,126 @@
+package com.baeldung.skippingfirstelement;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+public class SkipFirstElementExample {
+
+    private final List<String> stringList = new ArrayList<>();
+    private final Set<String> stringSet = new HashSet<>();
+    private final Map<String, String> stringMap = new HashMap<>();
+
+    public SkipFirstElementExample() {
+        // Initializing a List
+        stringList.add("Monday");
+        stringList.add("Tuesday");
+        stringList.add("Wednesday");
+        stringList.add("Thursday");
+        stringList.add("Friday");
+        stringList.add("Saturday");
+        stringList.add("Sunday");
+        // Initializing a Set
+        stringSet.add("Monday");
+        stringSet.add("Tuesday");
+        stringSet.add("Wednesday");
+        stringSet.add("Thursday");
+        stringSet.add("Friday");
+        stringSet.add("Saturday");
+        stringSet.add("Sunday");
+        // Initializing a Map
+        stringMap.put("Monday", "The day when coffee is a life support system.");
+        stringMap.put("Tuesday", "The day you realize that Monday's optimism was a lie.");
+        stringMap.put("Wednesday", "Hump Day, or as it's known, the 'Is it Friday yet?' day.");
+        stringMap.put("Thursday", "The day that says, 'Hold my beer, Friday is coming!'");
+        stringMap.put("Friday", "The golden child of the weekdays. The superhero of the workweek.");
+        stringMap.put("Saturday", "The day of rest? More like the day of 'What can I binge-watch next?'");
+        stringMap.put("Sunday", "The day before you have to adult again.");
+    }
+
+    void skippingFirstElementInListWithForLoop(List<String> stringList) {
+        for (int i = 1; i < stringList.size(); i++) {
+            process(stringList.get(i));
+        }
+    }
+
+    void skippingFirstElementInListWithWhileLoop(List<String> stringList) {
+        final Iterator<String> iterator = stringList.iterator();
+        if (iterator.hasNext()) {
+            iterator.next();
+        }
+        while (iterator.hasNext()) {
+            process(iterator.next());
+        }
+    }
+
+    void skippingFirstElementInSetWithWhileLoop(Set<String> stringSet) {
+        final Iterator<String> iterator = stringSet.iterator();
+        if (iterator.hasNext()) {
+            iterator.next();
+        }
+        while (iterator.hasNext()) {
+            process(iterator.next());
+        }
+    }
+
+    void skippingFirstElementInListWithWhileLoopStoringFirstElement(List<String> stringList) {
+        final Iterator<String> iterator = stringList.iterator();
+        String firstElement = null;
+        if (iterator.hasNext()) {
+            firstElement = iterator.next();
+        }
+        while (iterator.hasNext()) {
+            process(iterator.next());
+            // additional logic using fistElement
+        }
+    }
+
+    void skippingFirstElementInMapWithStreamSkip(Map<String, String> stringMap) {
+        stringMap.entrySet().stream().skip(1).forEach(this::process);
+    }
+
+    void skippingFirstElementInListWithSubList(List<String> stringList) {
+        for (final String element : stringList.subList(1, stringList.size())) {
+            process(element);
+        }
+    }
+
+    void skippingFirstElementInListWithForLoopWithAdditionalCheck(List<String> stringList) {
+        for (int i = 0; i < stringList.size(); i++) {
+            if (i == 0) {
+                // do something else
+            } else {
+                process(stringList.get(i));
+            }
+        }
+    }
+
+    void skippingFirstElementInListWithWhileLoopWithCounter(List<String> stringList) {
+        int counter = 0;
+        while (counter < stringList.size()) {
+            if (counter != 0) {
+                process(stringList.get(counter));
+            }
+            ++counter;
+        }
+    }
+
+    void skippingFirstElementInListWithReduce(List<String> stringList) {
+        stringList.stream().reduce((skip, element) -> {
+            process(element);
+            return element;
+        });
+    }
+
+    protected void process(String string) {
+        System.out.println(string);
+    }
+    protected void process(Entry<String, String> mapEntry) {
+        System.out.println(mapEntry);
+    }
+}

core-java-modules/core-java-collections-5/src/test/java/com/baeldung/skippingfirstelement/SkipFirstElementExampleUnitTest.java

@@ -0,0 +1,122 @@
+package com.baeldung.skippingfirstelement;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Stream;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.condition.EnabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+@EnabledForJreRange(min = JRE.JAVA_9)
+class SkipFirstElementExampleUnitTest {
+
+    private static TestableSkipFirstElement testableSkip = new TestableSkipFirstElement();
+
+    @BeforeEach
+    void setup() {
+        testableSkip.reset();
+    }
+
+    private static Stream<Arguments> listProvider() {
+        return Stream.of(
+            Arguments.of(
+                List.of("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"),
+                List.of("Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"))
+        );
+    }
+
+    private static Stream<Arguments> mapProvider() {
+        return Stream.of(
+            Arguments.of(
+                Map.of(
+                    "Monday", "The day when coffee is a life support system.",
+                    "Tuesday", "The day you realize that Monday's optimism was a lie.",
+                    "Wednesday", "Hump Day, or as it's known, the 'Is it Friday yet?' day.",
+                    "Thursday", "The day that says, 'Hold my beer, Friday is coming!'",
+                    "Friday", "The golden child of the weekdays. The superhero of the workweek.",
+                    "Saturday", "The day of rest? More like the day of 'What can I binge-watch next?'",
+                    "Sunday", "The day before you have to adult again."
+                )
+            )
+        );
+    }
+
+    @ParameterizedTest
+    @MethodSource("listProvider")
+    void skippingFirstElementInListWithForLoop(List<String> input, List<String> expected) {
+        testableSkip.skippingFirstElementInListWithForLoop(input);
+        List<?> actual = testableSkip.getResult();
+        assertEquals(actual, expected);
+    }
+
+    @ParameterizedTest
+    @MethodSource("listProvider")
+    void skippingFirstElementInListWithWhileLoop(List<String> input, List<String> expected) {
+        testableSkip.skippingFirstElementInListWithWhileLoop(input);
+        List<?> actual = testableSkip.getResult();
+        assertEquals(actual, expected);
+    }
+
+    @ParameterizedTest
+    @MethodSource("listProvider")
+    void skippingFirstElementInSetWithWhileLoop(List<String> input) {
+        testableSkip.skippingFirstElementInSetWithWhileLoop(new HashSet<>(input));
+        Set<?> actual = new HashSet<>(testableSkip.getResult());
+        assertEquals(actual.size(), input.size() - 1);
+    }
+
+    @ParameterizedTest
+    @MethodSource("listProvider")
+    void skippingFirstElementInListWithWhileLoopStoringFirstElement(List<String> input, List<String> expected) {
+        testableSkip.skippingFirstElementInListWithWhileLoopStoringFirstElement(input);
+        List<?> actual = testableSkip.getResult();
+        assertEquals(actual, expected);
+    }
+
+    @ParameterizedTest
+    @MethodSource("mapProvider")
+    void skippingFirstElementInMapWithStreamSkip(Map<String, String> input) {
+        testableSkip.skippingFirstElementInMapWithStreamSkip(input);
+        List<?> actual = testableSkip.getResult();
+        assertEquals(actual.size(), input.size() - 1);
+    }
+
+    @ParameterizedTest
+    @MethodSource("listProvider")
+    void skippingFirstElementInListWithSubList(List<String> input, List<String> expected) {
+        testableSkip.skippingFirstElementInListWithSubList(input);
+        List<?> actual = testableSkip.getResult();
+        assertEquals(actual, expected);
+    }
+
+    @ParameterizedTest
+    @MethodSource("listProvider")
+    void skippingFirstElementInListWithForLoopWithAdditionalCheck(List<String> input, List<String> expected) {
+        testableSkip.skippingFirstElementInListWithForLoopWithAdditionalCheck(input);
+        List<?> actual = testableSkip.getResult();
+        assertEquals(actual, expected);
+    }
+
+    @ParameterizedTest
+    @MethodSource("listProvider")
+    void skippingFirstElementInListWithWhileLoopWithCounter(List<String> input, List<String> expected) {
+        testableSkip.skippingFirstElementInListWithWhileLoopWithCounter(input);
+        List<?> actual = testableSkip.getResult();
+        assertEquals(actual, expected);
+    }
+
+    @ParameterizedTest
+    @MethodSource("listProvider")
+    void skippingFirstElementInListWithReduce(List<String> input, List<String> expected) {
+        testableSkip.skippingFirstElementInListWithReduce(input);
+        List<?> actual = testableSkip.getResult();
+        assertEquals(actual, expected);
+    }
+}

core-java-modules/core-java-collections-5/src/test/java/com/baeldung/skippingfirstelement/TestableSkip.java

@@ -0,0 +1,10 @@
+package com.baeldung.skippingfirstelement;
+
+import java.util.List;
+
+public interface TestableSkip {
+
+    void reset();
+
+    List<?> getResult();
+}

core-java-modules/core-java-collections-5/src/test/java/com/baeldung/skippingfirstelement/TestableSkipFirstElement.java

@@ -0,0 +1,37 @@
+package com.baeldung.skippingfirstelement;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map.Entry;
+
+public class TestableSkipFirstElement extends SkipFirstElementExample implements TestableSkip {
+
+
+    private List<String> processedList = new ArrayList<>();
+    private List<Entry<String, String>> processedEntryList = new ArrayList<>();
+
+    @Override
+    public void process(String string) {
+        processedList.add(string);
+    }
+
+    @Override
+    public void process(Entry<String, String> stringEntry) {
+        processedEntryList.add(stringEntry);
+    }
+
+    @Override
+    public void reset() {
+        processedList.clear();
+        processedEntryList.clear();
+    }
+
+    @Override
+    public List<?> getResult() {
+        if (!processedList.isEmpty())
+            return processedList;
+        return processedEntryList;
+    }
+
+
+}

core-java-modules/core-java-collections-array-list-2/README.md

@@ -0,0 +1,6 @@
+## Core Java Collections ArrayList
+
+This module contains articles about the Java ArrayList collection
+
+### Relevant Articles:
+- [Create an ArrayList with Multiple Object Types](https://www.baeldung.com/arraylist-with-multiple-object-types)

core-java-modules/core-java-collections-array-list-2/pom.xml

@@ -0,0 +1,32 @@
+<project
+    xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-collections-array-list-2</artifactId>
+    <name>core-java-collections-array-list-2</name>
+    <packaging>jar</packaging>
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+    
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>${maven-compiler-plugin.source}</source>
+                    <target>${maven-compiler-plugin.target}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+    
+    <properties>
+        <maven-compiler-plugin.source>17</maven-compiler-plugin.source>
+        <maven-compiler-plugin.target>17</maven-compiler-plugin.target>
+    </properties>
+</project>

core-java-modules/core-java-collections-array-list-2/src/main/java/com/baeldung/list/multipleobjecttypes/AlternativeMultipeTypeList.java

@@ -0,0 +1,51 @@
+package com.baeldung.list.multipleobjecttypes;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.function.Predicate;
+
+public class AlternativeMultipeTypeList {
+
+    public static void main(String[] args) {
+        // List of Parent Class
+        ArrayList<Number> myList = new ArrayList<>();
+        myList.add(1.2);
+        myList.add(2);
+        myList.add(-3.5);
+
+        // List of Interface type
+        ArrayList<Map> diffMapList = new ArrayList<>();
+        diffMapList.add(new HashMap<>());
+        diffMapList.add(new TreeMap<>());
+        diffMapList.add(new LinkedHashMap<>());
+
+        // List of Custom Object
+        ArrayList<CustomObject> objList = new ArrayList<>();
+        objList.add(new CustomObject("String"));
+        objList.add(new CustomObject(2));
+
+        // List via Functional Interface
+        List<Object> dataList = new ArrayList<>();
+
+        Predicate<Object> myPredicate = inputData -> (inputData instanceof String || inputData instanceof Integer);
+
+        UserFunctionalInterface myInterface = (listObj, data) -> {
+            if (myPredicate.test(data))
+                listObj.add(data);
+            else
+                System.out.println("Skipping input as data not allowed for class: " + data.getClass()
+                    .getSimpleName());
+            return listObj;
+        };
+
+        myInterface.addToList(dataList, Integer.valueOf(2));
+        myInterface.addToList(dataList, Double.valueOf(3.33));
+        myInterface.addToList(dataList, "String Value");
+        myInterface.printList(dataList);
+    }
+
+}

core-java-modules/core-java-collections-array-list-2/src/main/java/com/baeldung/list/multipleobjecttypes/CustomObject.java

@@ -0,0 +1,22 @@
+package com.baeldung.list.multipleobjecttypes;
+
+public class CustomObject {
+    String classData;
+    Integer intData;
+
+    CustomObject(String classData) {
+        this.classData = classData;
+    }
+
+    CustomObject(Integer intData) {
+        this.intData = intData;
+    }
+
+    public String getClassData() {
+        return this.classData;
+    }
+
+    public Integer getIntData() {
+        return this.intData;
+    }
+}

core-java-modules/core-java-collections-array-list-2/src/main/java/com/baeldung/list/multipleobjecttypes/MultipleObjectTypeArrayList.java

@@ -0,0 +1,40 @@
+package com.baeldung.list.multipleobjecttypes;
+
+import java.math.BigInteger;
+import java.time.LocalDate;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class MultipleObjectTypeArrayList {
+
+    public static void main(String[] args) {
+
+        ArrayList<Object> multiTypeList = new ArrayList<>();
+
+        multiTypeList.add(Integer.valueOf(10));
+        multiTypeList.add(Double.valueOf(11.5));
+        multiTypeList.add("String Data");
+        multiTypeList.add(Arrays.asList(1, 2, 3));
+        multiTypeList.add(new CustomObject("Class Data"));
+        multiTypeList.add(BigInteger.valueOf(123456789));
+        multiTypeList.add(LocalDate.of(2023, 9, 19));
+
+        for (Object dataObj : multiTypeList) {
+            if (dataObj instanceof Integer intData)
+                System.out.println("Integer Data : " + intData);
+            else if (dataObj instanceof Double doubleData)
+                System.out.println("Double Data : " + doubleData);
+            else if (dataObj instanceof String stringData)
+                System.out.println("String Data : " + stringData);
+            else if (dataObj instanceof List<?> intList)
+                System.out.println("List Data : " + intList);
+            else if (dataObj instanceof CustomObject customObj)
+                System.out.println("CustomObject Data : " + customObj.getClassData());
+            else if (dataObj instanceof BigInteger bigIntData)
+                System.out.println("BigInteger Data : " + bigIntData);
+            else if (dataObj instanceof LocalDate localDate)
+                System.out.println("LocalDate Data : " + localDate.toString());
+        }
+    }
+}

core-java-modules/core-java-collections-array-list-2/src/main/java/com/baeldung/list/multipleobjecttypes/UserFunctionalInterface.java

@@ -0,0 +1,18 @@
+package com.baeldung.list.multipleobjecttypes;
+
+import java.util.List;
+
+@FunctionalInterface
+public interface UserFunctionalInterface {
+
+    List<Object> addToList(List<Object> list, Object data);
+
+    default void printList(List<Object> dataList) {
+        for (Object data : dataList) {
+            if (data instanceof String stringData)
+                System.out.println("String Data: " + stringData);
+            if (data instanceof Integer intData)
+                System.out.println("Integer Data: " + intData);
+        }
+    }
+}