Merge remote-tracking branch 'origin/PR-6910' into PR-6910

# Conflicts:
#	spring-boot-modules/spring-boot-3/pom.xml

.github/ISSUE_TEMPLATE/issue_report.md

@@ -0,0 +1,32 @@
+---
+name: Issue Report
+about: Report an issue to help us improve
+title: '[ISSUE] '
+---
+
+**Article and Module Links**
+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.
+
+**To Reproduce**
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error
+
+**Expected Behavior**
+A clear and concise description of what you expected to happen.
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**Environment (please complete the following information):**
+- OS: [e.g. Windows]
+- Browser [e.g. chrome, safari]
+- Version [e.g. 22]
+
+**Additional Context**
+Add any other context about the issue here.

CONTRIBUTING.md

@@ -0,0 +1,11 @@
+# Contributing to Baeldung Tutorials
+First off, thank you for considering contributing to Baeldung Tutorials.
+
+## Reporting Issues
+Before you submit an issue, please review the guidelines below:
+
+1. **No Custom Modifications:** If your issue arises from any custom modifications you've made to the code in the repository, we won't be able to assist. We can only help if the issue is reproducible with the untouched codebase from this repo. If you're working with a modified version, consider asking for help on StackOverflow or other relevant forums.
+2. **Use a clear and descriptive title** for the issue to identify the problem.
+3. **Include a link to the article** you're having issues with.
+4. **Describe the exact steps which reproduce the problem** in as many details as possible.
+5. **Additional Details:** Offer any other context or descriptions that could be useful. Screenshots, error messages, copy/pasteable snippets, or logs can be immensely helpful.

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)

apache-poi-3/pom.xml

@@ -24,10 +24,74 @@
             <artifactId>poi-scratchpad</artifactId>
             <version>${poi.version}</version>
         </dependency>
+        <!-- https://mvnrepository.com/artifact/com.github.ozlerhakan/poiji -->
+        <dependency>
+            <groupId>com.github.ozlerhakan</groupId>
+            <artifactId>poiji</artifactId>
+            <version>${poiji.version}</version>
+        </dependency>
+
+        <!-- https://mvnrepository.com/artifact/org.apache.poi/poi/5.2.3 -->
+        <dependency>
+            <groupId>org.apache.poi</groupId>
+            <artifactId>poi</artifactId>
+            <version>${poi.version}</version>
+        </dependency>
+        <!-- https://mvnrepository.com/artifact/org.apache.poi/poi-ooxml-schemas/4.1.2 -->
+        <dependency>
+            <groupId>org.apache.poi</groupId>
+            <artifactId>poi-ooxml-schemas</artifactId>
+            <version>4.1.2</version>
+        </dependency>
+        <!-- https://mvnrepository.com/artifact/org.apache.xmlbeans/xmlbeans/5.1.1 -->
+        <dependency>
+            <groupId>org.apache.xmlbeans</groupId>
+            <artifactId>xmlbeans</artifactId>
+            <version>5.1.1</version>
+        </dependency>
+        <!-- https://mvnrepository.com/artifact/org.apache.commons/commons-collections4 -->
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>4.4</version>
+        </dependency>
+        <!-- https://mvnrepository.com/artifact/org.dhatim/fastexcel/0.15.7 -->
+        <dependency>
+            <groupId>org.dhatim</groupId>
+            <artifactId>fastexcel</artifactId>
+            <version>${fastexcel.version}</version>
+        </dependency>
+        <!-- https://mvnrepository.com/artifact/org.dhatim/fastexcel-reader/0.15.7 -->
+        <dependency>
+            <groupId>org.dhatim</groupId>
+            <artifactId>fastexcel-reader</artifactId>
+            <version>${fastexcel.version}</version>
+        </dependency>
+        <!-- https://mvnrepository.com/artifact/net.sourceforge.jexcelapi/jxl/2.6.12 -->
+        <dependency>
+            <groupId>net.sourceforge.jexcelapi</groupId>
+            <artifactId>jxl</artifactId>
+            <version>${jxl.version}</version>
+        </dependency>
+        <!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-api -->
+        <dependency>
+            <groupId>org.apache.logging.log4j</groupId>
+            <artifactId>log4j-api</artifactId>
+            <version>2.17.1</version>
+        </dependency>
+        <!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-core -->
+        <dependency>
+            <groupId>org.apache.logging.log4j</groupId>
+            <artifactId>log4j-core</artifactId>
+            <version>2.17.1</version>
+        </dependency>
     </dependencies>
 
     <properties>
         <poi.version>5.2.3</poi.version>
+        <poiji.version>4.1.1</poiji.version>
+        <fastexcel.version>0.15.7</fastexcel.version>
+        <jxl.version>2.6.12</jxl.version>
     </properties>
 
 </project>

apache-poi-3/src/main/java/com/baeldung/convert/exceldatatolist/FoodInfo.java

@@ -0,0 +1,54 @@
+package com.baeldung.convert.exceldatatolist;
+
+import com.poiji.annotation.ExcelCellName;
+
+public class FoodInfo {
+
+    @ExcelCellName("Category")
+    private String category; //food category
+    @ExcelCellName("Name")
+    private String name; // food name
+    @ExcelCellName("Measure")
+    private String measure;
+    @ExcelCellName("Calories")
+    private double calories; //amount of calories in kcal/measure
+
+    @Override
+    public String toString() {
+        return "FoodInfo{" + "category='" + category + '\'' + ", name='" + name + '\'' + ", measure='" + measure + '\'' + ", calories=" + calories + "} \n";
+    }
+
+
+    public String getCategory() {
+        return category;
+    }
+
+    public void setCategory(String category) {
+        this.category = category;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getMeasure() {
+        return measure;
+    }
+
+    public void setMeasure(String measure) {
+        this.measure = measure;
+    }
+
+    public double getCalories() {
+        return calories;
+    }
+
+    public void setCalories(double calories) {
+        this.calories = calories;
+    }
+
+}

apache-poi-3/src/main/java/com/baeldung/convert/exceldatatolist/fastexcel/ExcelDataToListOfObjectsFastExcel.java

@@ -0,0 +1,42 @@
+package com.baeldung.convert.exceldatatolist.fastexcel;
+
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.stream.Stream;
+
+import org.dhatim.fastexcel.reader.ReadableWorkbook;
+import org.dhatim.fastexcel.reader.Row;
+import org.dhatim.fastexcel.reader.Sheet;
+
+import com.baeldung.convert.exceldatatolist.FoodInfo;
+
+public class ExcelDataToListOfObjectsFastExcel {
+    public static List<FoodInfo> excelDataToListOfObjets_withFastExcel(String fileLocation)throws IOException, NumberFormatException {
+        List<FoodInfo> foodData = new ArrayList<FoodInfo>();
+
+        try (FileInputStream file = new FileInputStream(fileLocation);
+            ReadableWorkbook wb = new ReadableWorkbook(file)) {
+            Sheet sheet = wb.getFirstSheet();
+            for (Row row:
+                sheet.read()
+            ) {
+                if(row.getRowNum() == 1) {
+                    continue;
+                }
+                FoodInfo food = new FoodInfo();
+                food.setCategory(row.getCellText(0));
+                food.setName(row.getCellText(1));
+                food.setMeasure(row.getCellText(2));
+                food.setCalories(Double.parseDouble(row.getCellText(3)));
+
+                foodData.add(food);
+
+            }
+        }
+
+        return foodData;
+    }
+}

apache-poi-3/src/main/java/com/baeldung/convert/exceldatatolist/jexcelapi/ExcelDataToListOfObjectsJxl.java

@@ -0,0 +1,37 @@
+package com.baeldung.convert.exceldatatolist.jexcelapi;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import com.baeldung.convert.exceldatatolist.FoodInfo;
+
+import jxl.Sheet;
+import jxl.Workbook;
+import jxl.read.biff.BiffException;
+
+public class ExcelDataToListOfObjectsJxl {
+    public static List<FoodInfo> excelDataToListOfObjets_withJxl(String fileLocation) throws IOException, BiffException {
+
+        List<FoodInfo> foodData = new ArrayList<FoodInfo>();
+
+        Workbook workbook = Workbook.getWorkbook(new File(fileLocation));
+        Sheet sheet = workbook.getSheet(0);
+
+        int rows = sheet.getRows();
+
+        for (int i = 1; i < rows; i++) {
+            FoodInfo foodInfo = new FoodInfo();
+
+            foodInfo.setCategory(sheet.getCell(0, i).getContents());
+            foodInfo.setName(sheet.getCell(1, i).getContents());
+            foodInfo.setMeasure(sheet.getCell(2, i).getContents());
+            foodInfo.setCalories(Double.parseDouble(sheet.getCell(3, i).getContents()));
+           
+            foodData.add(foodInfo);
+
+        }
+        return foodData;
+    }
+}

apache-poi-3/src/main/java/com/baeldung/convert/exceldatatolist/poi/ExcelDataToListApachePOI.java

@@ -0,0 +1,39 @@
+package com.baeldung.convert.exceldatatolist.poi;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.poi.ss.usermodel.DataFormatter;
+import org.apache.poi.ss.usermodel.Row;
+import org.apache.poi.ss.usermodel.Sheet;
+import org.apache.poi.ss.usermodel.Workbook;
+import org.apache.poi.xssf.usermodel.XSSFWorkbook;
+
+import com.baeldung.convert.exceldatatolist.FoodInfo;
+
+public class ExcelDataToListApachePOI {
+    public static List<FoodInfo> excelDataToListOfObjets_withApachePOI(String fileLocation) throws IOException {
+        FileInputStream file = new FileInputStream(new File(fileLocation));
+        Workbook workbook = new XSSFWorkbook(file);
+        Sheet sheet = workbook.getSheetAt(0);
+        List<FoodInfo> foodData = new ArrayList<FoodInfo>();
+        DataFormatter dataFormatter = new DataFormatter();
+        for (int n = 1; n < sheet.getPhysicalNumberOfRows(); n++) {
+            Row row = sheet.getRow(n);
+            FoodInfo foodInfo = new FoodInfo();
+            int i = row.getFirstCellNum();
+
+            foodInfo.setCategory(dataFormatter.formatCellValue(row.getCell(i)));
+            foodInfo.setName(dataFormatter.formatCellValue(row.getCell(++i)));
+            foodInfo.setMeasure(dataFormatter.formatCellValue(row.getCell(++i)));
+            foodInfo.setCalories(Double.parseDouble(dataFormatter.formatCellValue(row.getCell(++i))));
+
+            foodData.add(foodInfo);
+
+        }
+        return foodData;
+    }
+}

apache-poi-3/src/main/java/com/baeldung/convert/exceldatatolist/poiji/ExcelDataToListOfObjectsPOIJI.java

@@ -0,0 +1,13 @@
+package com.baeldung.convert.exceldatatolist.poiji;
+
+import java.io.File;
+import java.util.List;
+
+import com.baeldung.convert.exceldatatolist.FoodInfo;
+import com.poiji.bind.Poiji;
+
+public class ExcelDataToListOfObjectsPOIJI {
+    public static List<FoodInfo> excelDataToListOfObjets_withPOIJI(String fileLocation){
+        return Poiji.fromExcel(new File(fileLocation), FoodInfo.class);
+    }
+}

apache-poi-3/src/test/java/com/baeldung/convert/exceldatatolist/ExcelDataToListOfObjectsUnitTest.java

@@ -0,0 +1,53 @@
+package com.baeldung.convert.exceldatatolist;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.IOException;
+import java.util.List;
+
+// import org.junit.jupiter.api.Test;
+// import static org.junit.jupiter.api.Assertions.*;
+import org.junit.Test;
+
+import com.baeldung.convert.exceldatatolist.fastexcel.ExcelDataToListOfObjectsFastExcel;
+import com.baeldung.convert.exceldatatolist.jexcelapi.ExcelDataToListOfObjectsJxl;
+import com.baeldung.convert.exceldatatolist.poi.ExcelDataToListApachePOI;
+import com.baeldung.convert.exceldatatolist.poiji.ExcelDataToListOfObjectsPOIJI;
+
+import jxl.read.biff.BiffException;
+
+public class ExcelDataToListOfObjectsUnitTest {
+
+    @Test
+    public void whenParsingExcelFileWithPOIJI_thenConvertsToList() throws IOException {
+        List<FoodInfo> foodInfoList = ExcelDataToListOfObjectsPOIJI.excelDataToListOfObjets_withPOIJI("src/main/resources/food_info.xlsx");
+
+        assertEquals("Beverages", foodInfoList.get(0).getCategory());
+        assertEquals("Dairy", foodInfoList.get(3).getCategory());
+    }
+
+    @Test
+    public void whenParsingExcelFileWithApachePOI_thenConvertsToList() throws IOException {
+        List<FoodInfo> foodInfoList = ExcelDataToListApachePOI.excelDataToListOfObjets_withApachePOI("src/main/resources/food_info.xlsx");
+
+        assertEquals("Beverages", foodInfoList.get(0).getCategory());
+        assertEquals("Dairy", foodInfoList.get(3).getCategory());
+    }
+
+    @Test
+    public void whenParsingExcelFileWithFastExcel_thenConvertsToList() throws IOException {
+        List<FoodInfo> foodInfoList = ExcelDataToListOfObjectsFastExcel.excelDataToListOfObjets_withFastExcel("src/main/resources/food_info.xlsx");
+
+        assertEquals("Beverages", foodInfoList.get(0).getCategory());
+        assertEquals("Dairy", foodInfoList.get(3).getCategory());
+    }
+
+    @Test
+    public void whenParsingExcelFileWithJxl_thenConvertsToList() throws IOException, BiffException {
+        List<FoodInfo> foodInfoList = ExcelDataToListOfObjectsJxl.excelDataToListOfObjets_withJxl("src/main/resources/food_info.xls");
+
+        assertEquals("Beverages", foodInfoList.get(0).getCategory());
+        assertEquals("Dairy", foodInfoList.get(3).getCategory());
+    }
+
+}

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

@@ -12,23 +12,36 @@
         <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.source.version}</source>-->
-<!--                    <target>{maven.compiler.target.version}</target>-->
-<!--                </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>
 
-<!--    <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>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>21</source>
+                    <target>21</target>
+                    <!-- 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>
 
 </project>

core-java-modules/core-java-21/src/main/java/com/baeldung/stringtemplates/StringCompositionTechniques.java

@@ -0,0 +1,37 @@
+package com.baeldung.stringtemplates;
+
+import java.text.MessageFormat;
+
+public class StringCompositionTechniques {
+    String composeUsingPlus(String feelsLike, String temperature, String unit) {
+        return "Today's weather is " + feelsLike + ", with a temperature of " + temperature + " degrees " + unit;
+    }
+
+    String composeUsingStringBuffer(String feelsLike, String temperature, String unit) {
+        return new StringBuffer().append("Today's weather is ")
+          .append(feelsLike)
+          .append(", with a temperature of ")
+          .append(temperature)
+          .append(" degrees ")
+          .append(unit)
+          .toString();
+    }
+
+    String composeUsingStringBuilder(String feelsLike, String temperature, String unit) {
+        return new StringBuilder().append("Today's weather is ")
+          .append(feelsLike)
+          .append(", with a temperature of ")
+          .append(temperature)
+          .append(" degrees ")
+          .append(unit)
+          .toString();
+    }
+
+    String composeUsingFormatters(String feelsLike, String temperature, String unit) {
+        return String.format("Today's weather is %s, with a temperature of %s degrees %s", feelsLike, temperature, unit);
+    }
+
+    String composeUsingMessageFormatter(String feelsLike, String temperature, String unit) {
+        return MessageFormat.format("Today''s weather is {0}, with a temperature of {1} degrees {2}", feelsLike, temperature, unit);
+    }
+}

core-java-modules/core-java-21/src/main/java/com/baeldung/stringtemplates/StringTemplateExamples.java

@@ -0,0 +1,56 @@
+package com.baeldung.stringtemplates;
+
+import static java.lang.StringTemplate.RAW;
+import static java.util.FormatProcessor.FMT;
+
+public class StringTemplateExamples {
+    String interpolationUsingSTRProcessor(String feelsLike, String temperature, String unit) {
+        return STR
+          . "Today's weather is \{ feelsLike }, with a temperature of \{ temperature } degrees \{ unit }" ;
+    }
+
+    String interpolationOfJSONBlock(String feelsLike, String temperature, String unit) {
+        return STR
+          . """
+          {
+            "feelsLike": "\{ feelsLike }",
+            "temperature": "\{ temperature }",
+            "unit": "\{ unit }"
+          }
+          """ ;
+    }
+
+    String interpolationWithExpressions() {
+        return STR
+          . "Today's weather is \{ getFeelsLike() }, with a temperature of \{ getTemperature() } degrees \{ getUnit() }" ;
+    }
+
+    String interpolationWithTemplates() {
+        StringTemplate str = RAW
+          . "Today's weather is \{ getFeelsLike() }, with a temperature of \{ getTemperature() } degrees \{ getUnit() }" ;
+        return STR.process(str);
+    }
+
+    String interpolationOfJSONBlockWithFMT(String feelsLike, float temperature, String unit) {
+        return FMT
+          . """
+      {
+        "feelsLike": "%1s\{ feelsLike }",
+        "temperature": "%2.2f\{ temperature }",
+        "unit": "%1s\{ unit }"
+      }
+      """ ;
+    }
+
+    private String getFeelsLike() {
+        return "pleasant";
+    }
+
+    private String getTemperature() {
+        return "25";
+    }
+
+    private String getUnit() {
+        return "Celsius";
+    }
+}

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.stringtemplates/StringTemplatesUnitTest.java

@@ -0,0 +1,67 @@
+package com.baeldung.stringtemplates;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class StringTemplatesUnitTest {
+
+    @Test
+    public void whenStringConcat_thenReturnComposedString() {
+        StringCompositionTechniques stringCompositionTechniques = new StringCompositionTechniques();
+        Assert.assertEquals("Today's weather is pleasant, with a temperature of 25 degrees Celsius", stringCompositionTechniques.composeUsingPlus("pleasant", "25", "Celsius"));
+    }
+
+    @Test
+    public void whenStringBuffer_thenReturnComposedString() {
+        StringCompositionTechniques stringCompositionTechniques = new StringCompositionTechniques();
+        Assert.assertEquals("Today's weather is pleasant, with a temperature of 25 degrees Celsius", stringCompositionTechniques.composeUsingStringBuffer("pleasant", "25", "Celsius"));
+    }
+
+    @Test
+    public void whenStringBuilder_thenReturnComposedString() {
+        StringCompositionTechniques stringCompositionTechniques = new StringCompositionTechniques();
+        Assert.assertEquals("Today's weather is pleasant, with a temperature of 25 degrees Celsius", stringCompositionTechniques.composeUsingStringBuilder("pleasant", "25", "Celsius"));
+    }
+
+    @Test
+    public void whenStringFormatter_thenReturnComposedFormattedString() {
+        StringCompositionTechniques stringCompositionTechniques = new StringCompositionTechniques();
+        Assert.assertEquals("Today's weather is pleasant, with a temperature of 25 degrees Celsius", stringCompositionTechniques.composeUsingFormatters("pleasant", "25", "Celsius"));
+    }
+
+    @Test
+    public void whenMessageFormatter_thenReturnComposedFormattedString() {
+        StringCompositionTechniques stringCompositionTechniques = new StringCompositionTechniques();
+        Assert.assertEquals("Today's weather is pleasant, with a temperature of 25 degrees Celsius", stringCompositionTechniques.composeUsingMessageFormatter("pleasant", "25", "Celsius"));
+    }
+
+    @Test
+    public void whenUsingStringTemplateSTR_thenReturnInterpolatedString() {
+        StringTemplateExamples templateExamples = new StringTemplateExamples();
+        Assert.assertEquals("Today's weather is pleasant, with a temperature of 25 degrees Celsius", templateExamples.interpolationUsingSTRProcessor("pleasant", "25", "Celsius"));
+    }
+
+    @Test
+    public void whenUsingMultilineStringTemplateSTR_thenReturnInterpolatedString() {
+        StringTemplateExamples templateExamples = new StringTemplateExamples();
+        Assert.assertEquals("{\n" + "  \"feelsLike\": \"pleasant\",\n" + "  \"temperature\": \"25\",\n" + "  \"unit\": \"Celsius\"\n" + "}\n", templateExamples.interpolationOfJSONBlock("pleasant", "25", "Celsius"));
+    }
+
+    @Test
+    public void whenUsingExpressionSTR_thenReturnInterpolatedString() {
+        StringTemplateExamples templateExamples = new StringTemplateExamples();
+        Assert.assertEquals("Today's weather is pleasant, with a temperature of 25 degrees Celsius", templateExamples.interpolationWithExpressions());
+    }
+
+    @Test
+    public void whenUsingExpressionRAW_thenReturnInterpolatedString() {
+        StringTemplateExamples templateExamples = new StringTemplateExamples();
+        Assert.assertEquals("Today's weather is pleasant, with a temperature of 25 degrees Celsius", templateExamples.interpolationWithTemplates());
+    }
+
+    @Test
+    public void whenUsingExpressionFMT_thenReturnInterpolatedString() {
+        StringTemplateExamples templateExamples = new StringTemplateExamples();
+        Assert.assertEquals("{\n" + "  \"feelsLike\": \"pleasant\",\n" + "  \"temperature\": \"25.86\",\n" + "  \"unit\": \"Celsius\"\n" + "}\n", templateExamples.interpolationOfJSONBlockWithFMT("pleasant", 25.8636F, "Celsius"));
+    }
+}

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-8-datetime/src/test/java/com/baeldung/dateapi/JavaDurationUnitTest.java

@@ -3,9 +3,11 @@ package com.baeldung.dateapi;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.time.Duration;
 import java.time.Instant;
+import java.time.LocalDateTime;
 import java.time.LocalTime;
 import java.time.temporal.ChronoUnit;
 
@@ -19,7 +21,7 @@ public class JavaDurationUnitTest {
         LocalTime finalTime = initialTime.plus(Duration.ofSeconds(30));
 
         long seconds = Duration.between(initialTime, finalTime)
-            .getSeconds();
+          .getSeconds();
 
         assertThat(seconds).isEqualTo(30);
     }
@@ -34,6 +36,22 @@ public class JavaDurationUnitTest {
         assertThat(seconds).isEqualTo(30);
     }
 
+    @Test
+    public void givenADuration_whenCallingisZeroAndisNegative_thenGetExpectedResult() {
+        LocalDateTime start = LocalDateTime.parse("2020-01-01T08:00:00");
+        LocalDateTime end = LocalDateTime.parse("2020-01-01T12:00:00");
+        assertFalse(Duration.between(start, end)
+          .isNegative());
+        assertTrue(Duration.between(end, start)
+          .isNegative());
+
+        LocalDateTime theTime = LocalDateTime.parse("2023-09-09T08:00:00");
+        assertTrue(Duration.between(theTime, theTime)
+          .isZero());
+        assertFalse(Duration.between(theTime, theTime)
+          .isNegative());
+    }
+
     @Test
     public void test2() {
         Instant start = Instant.parse("2017-10-03T10:15:30.00Z");
@@ -53,17 +71,17 @@ public class JavaDurationUnitTest {
         assertEquals(1, fromMinutes.toHours());
 
         assertEquals(120, duration.plusSeconds(60)
-            .getSeconds());
+          .getSeconds());
         assertEquals(30, duration.minusSeconds(30)
-            .getSeconds());
+          .getSeconds());
 
         assertEquals(120, duration.plus(60, ChronoUnit.SECONDS)
-            .getSeconds());
+          .getSeconds());
         assertEquals(30, duration.minus(30, ChronoUnit.SECONDS)
-            .getSeconds());
+          .getSeconds());
 
         Duration fromChar1 = Duration.parse("P1DT1H10M10.5S");
         Duration fromChar2 = Duration.parse("PT10M");
     }
 
-}
+}

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)