Feature/bael 4662 sealed classes (#10224)

* BAEL-4662: Initial commit of new module

* BAEL-4662: Example with Records

* BAEL-4662: Example with Interface

* BAEL-4662: Add test classes

* BAEL-4662: Update examples and tests

* BAEL-4662: Rename test classes

core-java-modules/core-java-15/.mvn/jvm.config

@@ -0,0 +1 @@
+--enable-preview

core-java-modules/core-java-15/README.md

@@ -0,0 +1,7 @@
+## Core Java 15
+
+This module contains articles about Java 15. 
+
+### Relevant articles
+
+- TODO: add article links here

core-java-modules/core-java-15/pom.xml

@@ -0,0 +1,77 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project
+    xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-15</artifactId>
+    <name>core-java-15</name>
+    <packaging>jar</packaging>
+    <url>http://maven.apache.org</url>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>../../pom.xml</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${apache-commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <version>${junit-jupiter.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <version>${junit-jupiter.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <release>${maven.compiler.release}</release>
+                    <compilerArgs>--enable-preview</compilerArgs>
+                    <source>15</source>
+                    <target>15</target>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>${surefire.plugin.version}</version>
+                <configuration>
+                    <argLine>--enable-preview</argLine>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <maven.compiler.release>15</maven.compiler.release>
+        <apache-commons-lang3.version>3.11</apache-commons-lang3.version>
+        <assertj.version>3.17.2</assertj.version>
+        <maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
+        <surefire.plugin.version>3.0.0-M3</surefire.plugin.version>
+    </properties>
+
+</project>

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/alternative/Vehicles.java

@@ -0,0 +1,49 @@
+package com.baeldung.sealed.alternative;
+
+public class Vehicles {
+
+    abstract static class Vehicle {
+
+        private final String registrationNumber;
+
+        public Vehicle(String registrationNumber) {
+            this.registrationNumber = registrationNumber;
+        }
+
+        public String getRegistrationNumber() {
+            return registrationNumber;
+        }
+
+    }
+
+    public static final class Car extends Vehicle {
+
+        private final int numberOfSeats;
+
+        public Car(int numberOfSeats, String registrationNumber) {
+            super(registrationNumber);
+            this.numberOfSeats = numberOfSeats;
+        }
+
+        public int getNumberOfSeats() {
+            return numberOfSeats;
+        }
+
+    }
+
+    public static final class Truck extends Vehicle {
+
+        private final int loadCapacity;
+
+        public Truck(int loadCapacity, String registrationNumber) {
+            super(registrationNumber);
+            this.loadCapacity = loadCapacity;
+        }
+
+        public int getLoadCapacity() {
+            return loadCapacity;
+        }
+
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/classes/Car.java

@@ -0,0 +1,21 @@
+package com.baeldung.sealed.classes;
+
+public non-sealed class Car extends Vehicle implements Service {
+
+    private final int numberOfSeats;
+
+    public Car(int numberOfSeats, String registrationNumber) {
+        super(registrationNumber);
+        this.numberOfSeats = numberOfSeats;
+    }
+
+    public int getNumberOfSeats() {
+        return numberOfSeats;
+    }
+
+    @Override
+    public int getMaxServiceIntervalInMonths() {
+        return 12;
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/classes/Service.java

@@ -0,0 +1,11 @@
+package com.baeldung.sealed.classes;
+
+public sealed interface Service permits Car, Truck {
+
+    int getMaxServiceIntervalInMonths();
+
+    default int getMaxDistanceBetweenServicesInKilometers() {
+        return 100000;
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/classes/Truck.java

@@ -0,0 +1,21 @@
+package com.baeldung.sealed.classes;
+
+public final class Truck extends Vehicle implements Service {
+
+    private final int loadCapacity;
+
+    public Truck(int loadCapacity, String registrationNumber) {
+        super(registrationNumber);
+        this.loadCapacity = loadCapacity;
+    }
+
+    public int getLoadCapacity() {
+        return loadCapacity;
+    }
+
+    @Override
+    public int getMaxServiceIntervalInMonths() {
+        return 18;
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/classes/Vehicle.java

@@ -0,0 +1,15 @@
+package com.baeldung.sealed.classes;
+
+public abstract sealed class Vehicle permits Car, Truck {
+
+    protected final String registrationNumber;
+
+    public Vehicle(String registrationNumber) {
+        this.registrationNumber = registrationNumber;
+    }
+
+    public String getRegistrationNumber() {
+        return registrationNumber;
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/records/Car.java

@@ -0,0 +1,14 @@
+package com.baeldung.sealed.records;
+
+public record Car(int numberOfSeats, String registrationNumber) implements Vehicle {
+
+    @Override
+    public String getRegistrationNumber() {
+        return registrationNumber;
+    }
+
+    public int getNumberOfSeats() {
+        return numberOfSeats;
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/records/Truck.java

@@ -0,0 +1,14 @@
+package com.baeldung.sealed.records;
+
+public record Truck(int loadCapacity, String registrationNumber) implements Vehicle {
+
+    @Override
+    public String getRegistrationNumber() {
+        return registrationNumber;
+    }
+
+    public int getLoadCapacity() {
+        return loadCapacity;
+    }
+
+}

core-java-modules/core-java-15/src/main/java/com/baeldung/sealed/records/Vehicle.java

@@ -0,0 +1,7 @@
+package com.baeldung.sealed.records;
+
+public sealed interface Vehicle permits Car, Truck {
+
+    String getRegistrationNumber();
+
+}

core-java-modules/core-java-15/src/test/java/com/baeldung/sealed/classes/VehicleUnitTest.java

@@ -0,0 +1,76 @@
+package com.baeldung.sealed.classes;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.lang.constant.ClassDesc;
+
+public class VehicleUnitTest {
+
+    private static Vehicle car;
+    private static Vehicle truck;
+
+    @BeforeAll
+    public static void createInstances() {
+        car = new Car(5, "VZ500DA");
+        truck = new Truck(19000, "VZ600TA");
+    }
+
+    @Test
+    public void givenCar_whenUsingReflectionAPI_thenSuperClassIsSealed() {
+        Assertions.assertThat(car.getClass().isSealed()).isEqualTo(false);
+        Assertions.assertThat(car.getClass().getSuperclass().isSealed()).isEqualTo(true);
+        Assertions.assertThat(car.getClass().getSuperclass().permittedSubclasses())
+                .contains(ClassDesc.of(car.getClass().getCanonicalName()));
+    }
+
+    @Test
+    public void givenTruck_whenUsingReflectionAPI_thenSuperClassIsSealed() {
+        Assertions.assertThat(truck.getClass().isSealed()).isEqualTo(false);
+        Assertions.assertThat(truck.getClass().getSuperclass().isSealed()).isEqualTo(true);
+        Assertions.assertThat(truck.getClass().getSuperclass().permittedSubclasses())
+                .contains(ClassDesc.of(truck.getClass().getCanonicalName()));
+    }
+
+    @Test
+    public void givenCar_whenGettingPropertyTraditionalWay_thenNumberOfSeatsPropertyIsReturned() {
+        Assertions.assertThat(getPropertyTraditionalWay(car)).isEqualTo(5);
+    }
+
+    @Test
+    public void givenCar_whenGettingPropertyViaPatternMatching_thenNumberOfSeatsPropertyIsReturned() {
+        Assertions.assertThat(getPropertyViaPatternMatching(car)).isEqualTo(5);
+    }
+
+    @Test
+    public void givenTruck_whenGettingPropertyTraditionalWay_thenLoadCapacityIsReturned() {
+        Assertions.assertThat(getPropertyTraditionalWay(truck)).isEqualTo(19000);
+    }
+
+    @Test
+    public void givenTruck_whenGettingPropertyViaPatternMatching_thenLoadCapacityIsReturned() {
+        Assertions.assertThat(getPropertyViaPatternMatching(truck)).isEqualTo(19000);
+    }
+
+    private int getPropertyTraditionalWay(Vehicle vehicle) {
+        if (vehicle instanceof Car) {
+            return ((Car) vehicle).getNumberOfSeats();
+        } else if (vehicle instanceof Truck) {
+            return ((Truck) vehicle).getLoadCapacity();
+        } else {
+            throw new RuntimeException("Unknown instance of Vehicle");
+        }
+    }
+
+    private int getPropertyViaPatternMatching(Vehicle vehicle) {
+        if (vehicle instanceof Car car) {
+            return car.getNumberOfSeats();
+        } else if (vehicle instanceof Truck truck) {
+            return truck.getLoadCapacity();
+        } else {
+            throw new RuntimeException("Unknown instance of Vehicle");
+        }
+    }
+
+}

core-java-modules/core-java-15/src/test/java/com/baeldung/sealed/records/VehicleUnitTest.java

@@ -0,0 +1,76 @@
+package com.baeldung.sealed.records;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.lang.constant.ClassDesc;
+
+public class VehicleUnitTest {
+
+    private static Vehicle car;
+    private static Vehicle truck;
+
+    @BeforeAll
+    public static void createInstances() {
+        car = new Car(4, "VZ500DA");
+        truck = new Truck(16000, "VZ600TA");
+    }
+
+    @Test
+    public void givenCar_whenUsingReflectionAPI_thenInterfaceIsSealed() {
+        Assertions.assertThat(car.getClass().isSealed()).isEqualTo(false);
+        Assertions.assertThat(car.getClass().getInterfaces()[0].isSealed()).isEqualTo(true);
+        Assertions.assertThat(car.getClass().getInterfaces()[0].permittedSubclasses())
+                .contains(ClassDesc.of(car.getClass().getCanonicalName()));
+    }
+
+    @Test
+    public void givenTruck_whenUsingReflectionAPI_thenInterfaceIsSealed() {
+        Assertions.assertThat(truck.getClass().isSealed()).isEqualTo(false);
+        Assertions.assertThat(truck.getClass().getInterfaces()[0].isSealed()).isEqualTo(true);
+        Assertions.assertThat(truck.getClass().getInterfaces()[0].permittedSubclasses())
+                .contains(ClassDesc.of(truck.getClass().getCanonicalName()));
+    }
+
+    @Test
+    public void givenCar_whenGettingPropertyTraditionalWay_thenNumberOfSeatsPropertyIsReturned() {
+        Assertions.assertThat(getPropertyTraditionalWay(car)).isEqualTo(4);
+    }
+
+    @Test
+    public void givenCar_whenGettingPropertyViaPatternMatching_thenNumberOfSeatsPropertyIsReturned() {
+        Assertions.assertThat(getPropertyViaPatternMatching(car)).isEqualTo(4);
+    }
+
+    @Test
+    public void givenTruck_whenGettingPropertyTraditionalWay_thenLoadCapacityIsReturned() {
+        Assertions.assertThat(getPropertyTraditionalWay(truck)).isEqualTo(16000);
+    }
+
+    @Test
+    public void givenTruck_whenGettingPropertyViaPatternMatching_thenLoadCapacityIsReturned() {
+        Assertions.assertThat(getPropertyViaPatternMatching(truck)).isEqualTo(16000);
+    }
+
+    private int getPropertyTraditionalWay(Vehicle vehicle) {
+        if (vehicle instanceof Car) {
+            return ((Car) vehicle).getNumberOfSeats();
+        } else if (vehicle instanceof Truck) {
+            return ((Truck) vehicle).getLoadCapacity();
+        } else {
+            throw new RuntimeException("Unknown instance of Vehicle");
+        }
+    }
+
+    private int getPropertyViaPatternMatching(Vehicle vehicle) {
+        if (vehicle instanceof Car car) {
+            return car.getNumberOfSeats();
+        } else if (vehicle instanceof Truck truck) {
+            return truck.getLoadCapacity();
+        } else {
+            throw new RuntimeException("Unknown instance of Vehicle");
+        }
+    }
+
+}