Merge branch 'master' of https://github.com/eugenp/tutorials into JAVA-1672

core-java-modules/core-java-17/pom.xml

@@ -23,6 +23,18 @@
             <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>
@@ -42,10 +54,13 @@
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-surefire-plugin</artifactId>
                 <version>${surefire.plugin.version}</version>
+
                 <configuration>
                     <argLine>--enable-preview</argLine>
+                    <argLine>--enable-native-access=core.java</argLine>
                     <forkCount>1</forkCount>
                 </configuration>
+
                 <dependencies>
                     <dependency>
                         <groupId>org.apache.maven.surefire</groupId>

core-java-modules/core-java-17/src/main/java/com/baeldung/features/JEP356.java

@@ -0,0 +1,20 @@
+package com.baeldung.features;
+
+import java.util.random.RandomGeneratorFactory;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+public class JEP356 {
+
+    public Stream<String> getAllAlgorithms() {
+        return RandomGeneratorFactory.all().map(RandomGeneratorFactory::name);
+    }
+
+    public IntStream getPseudoInts(String algorithm, int streamSize) {
+        // returns an IntStream with size @streamSize of random numbers generated using the @algorithm
+        // where the lower bound is 0 and the upper is 100 (exclusive)
+        return RandomGeneratorFactory.of(algorithm)
+                .create()
+                .ints(streamSize, 0,100);
+    }
+}

core-java-modules/core-java-17/src/main/java/com/baeldung/features/JEP406.java

@@ -0,0 +1,28 @@
+package com.baeldung.features;
+
+import com.baeldung.features.JEP409.Circle;
+import com.baeldung.features.JEP409.Shape;
+import com.baeldung.features.JEP409.Triangle;
+
+public class JEP406 {
+
+    static record Human (String name, int age, String profession) {}
+
+    public String checkObject(Object obj) {
+        return switch (obj) {
+            case Human h -> "Name: %s, age: %s and profession: %s".formatted(h.name(), h.age(), h.profession());
+            case Circle c -> "This is a circle";
+            case Shape s -> "It is just a shape";
+            case null -> "It is null";
+            default -> "It is an object";
+        };
+    }
+
+    public String checkShape(Shape shape) {
+        return switch (shape) {
+            case Triangle t && (t.getNumberOfSides() != 3) -> "This is a weird triangle";
+            case Circle c && (c.getNumberOfSides() != 0) -> "This is a weird circle";
+            default -> "Just a normal shape";
+        };
+    }
+}

core-java-modules/core-java-17/src/main/java/com/baeldung/features/JEP409.java

@@ -0,0 +1,38 @@
+package com.baeldung.features;
+
+public class JEP409 {
+
+    sealed interface Shape permits Rectangle, Circle, Square, Triangle {
+        int getNumberOfSides();
+    }
+
+    static final class Rectangle implements Shape {
+        @Override
+        public int getNumberOfSides() {
+            return 4;
+        }
+    }
+
+    static final class Circle implements Shape {
+        @Override
+        public int getNumberOfSides() {
+            return 0;
+        }
+    }
+
+    static final class Square implements Shape {
+        @Override
+        public int getNumberOfSides() {
+            return 4;
+        }
+    }
+
+    static non-sealed class Triangle implements Shape {
+
+        @Override
+        public int getNumberOfSides() {
+            return 3;
+        }
+    }
+
+}

core-java-modules/core-java-17/src/main/java/com/baeldung/features/JEP412.java

@@ -0,0 +1,56 @@
+package com.baeldung.features;
+
+import jdk.incubator.foreign.CLinker;
+import jdk.incubator.foreign.FunctionDescriptor;
+import jdk.incubator.foreign.MemoryAddress;
+import jdk.incubator.foreign.SymbolLookup;
+
+import java.io.IOException;
+import java.lang.invoke.MethodType;
+
+import static jdk.incubator.foreign.ResourceScope.newImplicitScope;
+
+public class JEP412 {
+
+    private static final SymbolLookup libLookup;
+
+    static {
+        var resource = JEP412.class.getResource("/compile_c.sh");
+        try {
+            var process = new ProcessBuilder("sh", resource.getPath()).start();
+            while (process.isAlive()) {}
+        } catch (IOException ex) {
+            throw new RuntimeException(ex);
+        }
+
+        var path = JEP412.class.getResource("/print_name.so").getPath();
+        System.load(path);
+        libLookup = SymbolLookup.loaderLookup();
+    }
+
+    public String getPrintNameFormat(String name){
+
+        var printMethod = libLookup.lookup("printName");
+
+        if (printMethod.isPresent()) {
+            var methodReference = CLinker.getInstance()
+                .downcallHandle(
+                    printMethod.get(),
+                    MethodType.methodType(MemoryAddress.class, MemoryAddress.class),
+                    FunctionDescriptor.of(CLinker.C_POINTER, CLinker.C_POINTER)
+                );
+
+            try {
+                var nativeString = CLinker.toCString(name, newImplicitScope());
+                var invokeReturn = methodReference.invoke(nativeString.address());
+                var memoryAddress = (MemoryAddress) invokeReturn;
+                return CLinker.toJavaString(memoryAddress);
+            } catch (Throwable throwable) {
+                throw new RuntimeException(throwable);
+            }
+        }
+        throw new RuntimeException("printName function not found.");
+    }
+}
+
+

core-java-modules/core-java-17/src/main/java/com/baeldung/features/JEP414.java

@@ -0,0 +1,27 @@
+package com.baeldung.features;
+
+import jdk.incubator.vector.FloatVector;
+import jdk.incubator.vector.VectorSpecies;
+
+public class JEP414 {
+
+    private static final VectorSpecies<Float> SPECIES = FloatVector.SPECIES_PREFERRED;
+
+
+    public void newVectorComputation(float[] a, float[] b, float[] c) {
+        for (var i = 0; i < a.length; i += SPECIES.length()) {
+            var m = SPECIES.indexInRange(i, a.length);
+            var va = FloatVector.fromArray(SPECIES, a, i, m);
+            var vb = FloatVector.fromArray(SPECIES, b, i, m);
+            var vc = va.mul(vb);
+            vc.intoArray(c, i, m);
+        }
+    }
+
+    public void commonVectorComputation(float[] a, float[] b, float[] c) {
+        for (var i = 0; i < a.length; i ++) {
+            c[i] = a[i] * b[i];
+        }
+    }
+
+}

core-java-modules/core-java-17/src/main/java/module-info.java

@@ -0,0 +1,4 @@
+module core.java {
+    requires jdk.incubator.vector;
+    requires jdk.incubator.foreign;
+}

core-java-modules/core-java-17/src/main/resources/compile_c.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+SCRIPTPATH="$( cd -- "$(dirname "$0")" >/dev/null 2>&1 ; pwd -P )"
+
+gcc -c -fPIC $SCRIPTPATH/print_name.c
+gcc -shared -rdynamic -o print_name.so print_name.o
+
+mv print_name.so $SCRIPTPATH/
+mv print_name.o $SCRIPTPATH/

core-java-modules/core-java-17/src/main/resources/print_name.c

@@ -0,0 +1,8 @@
+#include<stdio.h>
+#include<stdlib.h>
+
+char* printName(char *name) {
+    char* newString = (char*)malloc((15 + sizeof(name))*sizeof(char));
+    sprintf(newString, "Your name is %s", name);
+    return newString;
+}

core-java-modules/core-java-17/src/test/java/com/baeldung/features/JEP356UnitTest.java

@@ -0,0 +1,19 @@
+package com.baeldung.features;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class JEP356UnitTest {
+
+    @Test
+    void getPseudoInts_whenUsingAlgorithmXoroshiro128PlusPlus_shouldReturnStreamOfRandomInteger() {
+        var algorithm = "Xoshiro256PlusPlus";
+        var streamSize = 100;
+
+        JEP356 jep356 = new JEP356();
+
+        jep356.getPseudoInts(algorithm, streamSize)
+            .forEach(value -> assertThat(value).isLessThanOrEqualTo(99));
+    }
+}

core-java-modules/core-java-17/src/test/java/com/baeldung/features/JEP406UnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.features;
+
+import com.baeldung.features.JEP406.Human;
+import com.baeldung.features.JEP409.Square;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class JEP406UnitTest {
+
+    @Test
+    void checkObject_shouldMatchWithHuman() {
+        var jep406 = new JEP406();
+
+        var human = new Human("John", 31, "Developer");
+
+        var checkResult = jep406.checkObject(human);
+
+        assertEquals("Name: John, age: 31 and profession: Developer", checkResult);
+    }
+
+    @Test
+    void checkShape_shouldMatchWithShape() {
+        var jep406 = new JEP406();
+
+        var square = new Square();
+
+        var checkResult = jep406.checkShape(square);
+
+        assertEquals("Just a normal shape", checkResult);
+    }
+
+}

core-java-modules/core-java-17/src/test/java/com/baeldung/features/JEP409UnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.features;
+
+import com.baeldung.features.JEP409.*;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.verify;
+
+class JEP409UnitTest {
+
+    static class WeirdTriangle extends Triangle {
+        @Override public int getNumberOfSides() {
+            return 40;
+        }
+    }
+
+    @Test
+    void testSealedClass_shouldInvokeRightClass() {
+
+        Shape shape = spy(new WeirdTriangle());
+
+        int numberOfSides = getNumberOfSides(shape);
+
+        assertEquals(40, numberOfSides);
+        verify(shape).getNumberOfSides();
+    }
+
+    int getNumberOfSides(Shape shape) {
+        return switch (shape) {
+            case WeirdTriangle t -> t.getNumberOfSides();
+            case Circle c -> c.getNumberOfSides();
+            case Triangle t -> t.getNumberOfSides();
+            case Rectangle r -> r.getNumberOfSides();
+            case Square s -> s.getNumberOfSides();
+        };
+    }
+}

core-java-modules/core-java-17/src/test/java/com/baeldung/features/JEP412UnitTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.features;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class JEP412UnitTest {
+
+    @Test
+    void getPrintNameFormat_whenPassingAName_shouldReceiveItFormatted() {
+        var jep412 = new JEP412();
+
+        var formattedName = jep412.getPrintNameFormat("John");
+
+        assertEquals("Your name is John", formattedName);
+    }
+}

core-java-modules/core-java-17/src/test/java/com/baeldung/features/JEP414UnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.features;
+
+import org.junit.jupiter.api.Test;
+
+import static java.util.stream.Collectors.toList;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class JEP414UnitTest {
+
+    @Test
+    void vectorComputation_shouldMultiplyVectors() {
+        var jep414 = new JEP414();
+
+        float[] a = initArray(100);
+        float[] b = initArray(100);
+        float[] c = new float[100];
+        float[] d = new float[100];
+
+        jep414.newVectorComputation(a, b, c);
+        jep414.commonVectorComputation(a, b, d);
+
+        for (int i = 0; i < a.length; i++) {
+            assertEquals(c[i], d[i]);
+        }
+    }
+
+    private float[] initArray(int size) {
+        final var jep356 = new JEP356();
+        final var values = new float[size];
+        final var pseudoInts = jep356.getPseudoInts("Xoshiro256PlusPlus", size).mapToObj(Float::valueOf).collect(toList());
+
+        for (int i = 0; i < pseudoInts.size(); i++) {
+            values[i] = pseudoInts.get(i);
+        }
+
+        return values;
+    }
+}

core-java-modules/core-java-collections-maps-4/pom.xml

@@ -15,6 +15,27 @@
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 	
+	<properties>
+	    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+		<maven.compiler.source>1.8</maven.compiler.source>
+		<maven.compiler.target>1.8</maven.compiler.target>
+	</properties>
+
+	<dependencies>
+		<dependency>
+			<groupId>junit</groupId>
+			<artifactId>junit</artifactId>
+			<version>4.12</version>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.hamcrest</groupId>
+			<artifactId>hamcrest-all</artifactId>
+			<version>1.3</version>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+
 	<build>
 		<pluginManagement>
 			<plugins>

core-java-modules/core-java-collections-maps-4/src/main/java/com/baeldung/nestedhashmaps/Address.java

@@ -0,0 +1,32 @@
+package com.baeldung.nestedhashmaps;
+
+public class Address {
+
+    private Integer addressId;
+    private String addressLocation;
+
+    public Address() {
+    }
+
+    public Address(Integer addressId, String addressLocation) {
+        this.addressId = addressId;
+        this.addressLocation = addressLocation;
+    }
+
+    public Integer getAddressId() {
+        return addressId;
+    }
+
+    public void setAddressId(Integer addressId) {
+        this.addressId = addressId;
+    }
+
+    public String getAddressLocation() {
+        return addressLocation;
+    }
+
+    public void setAddressLocation(String addressLocation) {
+        this.addressLocation = addressLocation;
+    }
+
+}

core-java-modules/core-java-collections-maps-4/src/main/java/com/baeldung/nestedhashmaps/Employee.java

@@ -0,0 +1,43 @@
+package com.baeldung.nestedhashmaps;
+
+public class Employee {
+
+    private Integer employeeId;
+    private Address address;
+    private String employeeName;
+
+    public Employee() {
+        super();
+    }
+
+    public Employee(Integer employeeId, Address address, String employeeName) {
+        this.employeeId = employeeId;
+        this.address = address;
+        this.employeeName = employeeName;
+    }
+
+    public Integer getEmployeeId() {
+        return employeeId;
+    }
+
+    public void setEmployeeId(Integer employeeId) {
+        this.employeeId = employeeId;
+    }
+
+    public Address getAddress() {
+        return address;
+    }
+
+    public void setAddress(Address address) {
+        this.address = address;
+    }
+
+    public String getEmployeeName() {
+        return employeeName;
+    }
+
+    public void setEmployeeName(String employeeName) {
+        this.employeeName = employeeName;
+    }
+
+}

core-java-modules/core-java-collections-maps-4/src/main/java/com/baeldung/nestedhashmaps/MapsUtil.java

@@ -0,0 +1,57 @@
+package com.baeldung.nestedhashmaps;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.stream.Collectors;
+
+public class MapsUtil {
+
+    MapsUtil() {
+        super();
+    }
+
+    public Map<Integer, String> buildInnerMap(List<String> batterList) {
+        Map<Integer, String> innerBatterMap = new HashMap<Integer, String>();
+
+        int index = 1;
+        for (String item : batterList) {
+            innerBatterMap.put(index, item);
+            index++;
+        }
+
+        return innerBatterMap;
+    }
+
+    public Map<Integer, Map<String, String>> createNestedMapfromStream(List<Employee> listEmployee) {
+        Map<Integer, Map<String, String>> employeeAddressMap = listEmployee.stream()
+                .collect(Collectors.groupingBy(e -> e.getAddress().getAddressId(),
+                        Collectors.toMap(f -> f.getAddress().getAddressLocation(), Employee::getEmployeeName)));
+        return employeeAddressMap;
+    }
+
+    public Map<Integer, Map<Integer, Address>> createNestedObjectMap(List<Employee> listEmployee) {
+        Map<Integer, Map<Integer, Address>> employeeMap = new HashMap<>();
+
+        employeeMap = listEmployee.stream().collect(Collectors.groupingBy((Employee emp) -> emp.getEmployeeId(),
+                Collectors.toMap((Employee emp) -> emp.getAddress().getAddressId(), fEmpObj -> fEmpObj.getAddress())));
+
+        return employeeMap;
+    }
+
+    public Map<String, String> flattenMap(Map<?, ?> source) {
+        Map<String, String> converted = new HashMap<>();
+
+        for (Entry<?, ?> entry : source.entrySet()) {
+            if (entry.getValue() instanceof Map) {
+                flattenMap((Map<String, Object>) entry.getValue())
+                        .forEach((key, value) -> converted.put(entry.getKey() + "." + key, value));
+            } else {
+                converted.put(entry.getKey().toString(), entry.getValue().toString());
+            }
+        }
+        return converted;
+    }
+
+}

core-java-modules/core-java-collections-maps-4/src/main/java/com/baeldung/nestedhashmaps/NestedHashMapExamplesClass.java

@@ -0,0 +1,118 @@
+package com.baeldung.nestedhashmaps;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.Map;
+
+import java.util.List;
+
+public class NestedHashMapExamplesClass {
+    public static void main(String[] args) {
+
+        MapsUtil mUtil = new MapsUtil();
+
+        List<String> batterList = new ArrayList<>();
+        Map<String, Map<Integer, String>> outerBakedGoodsMap = new HashMap<>();
+        Map<String, Map<Integer, String>> outerBakedGoodsMap2 = new HashMap<>();
+        Map<String, Map<Integer, String>> outerBakedGoodsMap3 = new HashMap<>();
+        Map<String, Map<Integer, String>> outerBakedGoodsMap4 = new HashMap<>();
+
+        batterList.add("Mulberry");
+        batterList.add("Cranberry");
+        batterList.add("Blackberry");
+        batterList.add("Mixed fruit");
+        batterList.add("Orange");
+
+        outerBakedGoodsMap.put("Cake", mUtil.buildInnerMap(batterList));
+
+        batterList.clear();
+        batterList.add("Candy");
+        batterList.add("Dark Chocolate");
+        batterList.add("Chocolate");
+        batterList.add("Jam filled");
+        batterList.add("Pineapple");
+
+        outerBakedGoodsMap.put("Donut", mUtil.buildInnerMap(batterList));
+
+        outerBakedGoodsMap2.put("Eclair", mUtil.buildInnerMap(batterList));
+        outerBakedGoodsMap2.put("Donut", mUtil.buildInnerMap(batterList));
+
+        outerBakedGoodsMap3.put("Cake", mUtil.buildInnerMap(batterList));
+        batterList.clear();
+        batterList.add("Banana");
+        batterList.add("Red Velvet");
+        batterList.add("Blackberry");
+        batterList.add("Passion fruit");
+        batterList.add("Kiwi");
+
+        outerBakedGoodsMap3.put("Donut", mUtil.buildInnerMap(batterList));
+
+        outerBakedGoodsMap4.putAll(outerBakedGoodsMap);
+
+        System.out.println(outerBakedGoodsMap.equals(outerBakedGoodsMap2));
+        System.out.println(outerBakedGoodsMap.equals(outerBakedGoodsMap3));
+        System.out.println(outerBakedGoodsMap.equals(outerBakedGoodsMap4));
+
+        outerBakedGoodsMap.get("Cake")
+            .put(6, "Cranberry");
+        System.out.println(outerBakedGoodsMap);
+
+        outerBakedGoodsMap.get("Cake")
+            .remove(5);
+        System.out.println(outerBakedGoodsMap);
+
+        outerBakedGoodsMap.put("Eclair", new HashMap<Integer, String>() {
+            {
+                put(1, "Dark Chocolate");
+            }
+        });
+
+        System.out.println(outerBakedGoodsMap);
+        outerBakedGoodsMap.remove("Eclair");
+        System.out.println(outerBakedGoodsMap);
+        System.out.println("Baked Goods Map Flattened: " + mUtil.flattenMap(outerBakedGoodsMap));
+
+        // Employees Map
+        List<Employee> listEmployee = new ArrayList<Employee>();
+
+        listEmployee.add(new Employee(1, new Address(124, "Timbuktoo"), "Thorin Oakenshield"));
+        listEmployee.add(new Employee(2, new Address(100, "Misty Lanes"), "Balin"));
+        listEmployee.add(new Employee(3, new Address(156, "Bramles Lane"), "Bofur"));
+        listEmployee.add(new Employee(4, new Address(200, "Bag End"), "Bilbo Baggins"));
+        listEmployee.add(new Employee(5, new Address(23, "Rivendell"), "Elrond"));
+
+        Map<Integer, Map<String, String>> employeeAddressMap = mUtil.createNestedMapfromStream(listEmployee);
+
+        Map<Integer, Map<Integer, Address>> employeeMap = mUtil.createNestedObjectMap(listEmployee);
+        Map<Integer, Map<Integer, Address>> employeeMap2 = mUtil.createNestedObjectMap(listEmployee);
+
+        listEmployee.clear();
+        listEmployee.add(new Employee(1, new Address(500, "Timbuktoo"), "Thorin Oakenshield"));
+        listEmployee.add(new Employee(2, new Address(600, "Misty Lanes"), "Balin"));
+        listEmployee.add(new Employee(3, new Address(700, "Bramles Lane"), "Bofur"));
+        listEmployee.add(new Employee(4, new Address(800, "Bag End"), "Bilbo Baggins"));
+        listEmployee.add(new Employee(5, new Address(900, "Rivendell"), "Elrond"));
+
+        Map<Integer, Map<String, String>> employeeAddressMap1 = mUtil.createNestedMapfromStream(listEmployee);
+
+        Map<Integer, Map<Integer, Address>> employeeMap1 = mUtil.createNestedObjectMap(listEmployee);
+
+        System.out.println(employeeMap.equals(employeeMap1));
+        System.out.println(employeeMap.equals(employeeMap2));
+
+        for (Map.Entry<String, Map<Integer, String>> outerBakedGoodsMapEntrySet : outerBakedGoodsMap.entrySet()) {
+            Map<Integer, String> valueMap = outerBakedGoodsMapEntrySet.getValue();
+            System.out.println(valueMap.entrySet());
+        }
+
+        for (Map.Entry<Integer, Map<String, String>> employeeEntrySet : employeeAddressMap.entrySet()) {
+            Map<String, String> valueMap = employeeEntrySet.getValue();
+            System.out.println(valueMap.entrySet());
+        }
+
+        System.out.println("Employee Address Map Flattened: " + mUtil.flattenMap(employeeAddressMap));
+
+        System.out.println(employeeAddressMap.equals(employeeAddressMap1));
+    }
+
+}

core-java-modules/core-java-collections-maps-4/src/test/java/com/baeldung/nestedhashmaps/NestedHashMapExamplesClassUnitTest.java

@@ -0,0 +1,243 @@
+package com.baeldung.nestedhashmaps;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.CoreMatchers.notNullValue;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNotSame;
+import static org.junit.Assert.assertThat;
+import org.hamcrest.collection.IsMapContaining;
+
+public class NestedHashMapExamplesClassUnitTest {
+    private MapsUtil mUtil = new MapsUtil();
+    private List<String> batterList = new ArrayList<>();
+    private List<Employee> listEmployee = new ArrayList<Employee>();
+    private Map<String, Map<Integer, String>> actualBakedGoodsMap = new HashMap<>();
+    private Map<Integer, Map<String, String>> actualEmployeeAddressMap = new HashMap<>();
+    private Map<Integer, Map<Integer, Address>> actualEmployeeMap = new HashMap<>();
+
+    @Test
+    public void whenCreateNestedHashMap_thenNestedMap() {
+        assertThat(mUtil.buildInnerMap(batterList), is(notNullValue()));
+        Assert.assertEquals(actualBakedGoodsMap.keySet().size(), 2);
+        Assert.assertThat(actualBakedGoodsMap, IsMapContaining.hasValue(equalTo(mUtil.buildInnerMap(batterList))));
+    }
+
+    private Map<Integer, Map<String, String>> setup() {
+        Map<Integer, Map<String, String>> expectedMap = new HashMap<>();
+        expectedMap.put(Integer.valueOf(100), new HashMap<String, String>() {
+            {
+                put("Misty Lanes", "Balin");
+            }
+        });
+        expectedMap.put(Integer.valueOf(200), new HashMap<String, String>() {
+            {
+                put("Bag End", "Bilbo Baggins");
+            }
+        });
+        expectedMap.put(Integer.valueOf(156), new HashMap<String, String>() {
+            {
+                put("Brambles Lane", "Bofur");
+            }
+        });
+        expectedMap.put(Integer.valueOf(124), new HashMap<String, String>() {
+            {
+                put("Timbuktoo", "Thorin Oakenshield");
+            }
+        });
+        expectedMap.put(Integer.valueOf(23), new HashMap<String, String>() {
+            {
+                put("Rivendell", "Elrond");
+            }
+        });
+
+        return expectedMap;
+    }
+
+    @Test
+    public void whenCreateNestedHashMapwithStreams_thenNestedMap() {
+
+        Map<Integer, Map<String, String>> expectedMap = setup();
+
+        assertThat(actualEmployeeAddressMap, equalTo(expectedMap));
+    }
+
+    @Test
+    public void whenCompareTwoHashMapswithDifferenctValues_usingEquals_thenFail() {
+        Map<String, Map<Integer, String>> outerBakedGoodsMap2 = new HashMap<>();
+        outerBakedGoodsMap2.put("Eclair", mUtil.buildInnerMap(batterList));
+        outerBakedGoodsMap2.put("Donut", mUtil.buildInnerMap(batterList));
+        assertNotEquals(outerBakedGoodsMap2, actualBakedGoodsMap);
+
+        Map<String, Map<Integer, String>> outerBakedGoodsMap3 = new HashMap<String, Map<Integer, String>>();
+        outerBakedGoodsMap3.put("Cake", mUtil.buildInnerMap(batterList));
+        batterList = new ArrayList<>();
+        batterList = Arrays.asList("Banana", "Red Velvet", "Blackberry", "Passion fruit", "Kiwi");
+
+        outerBakedGoodsMap3.put("Donut", mUtil.buildInnerMap(batterList));
+
+        assertNotEquals(outerBakedGoodsMap2, actualBakedGoodsMap);
+
+        listEmployee.clear();
+        listEmployee.add(new Employee(1, new Address(500, "Timbuktoo"), "Thorin Oakenshield"));
+        listEmployee.add(new Employee(2, new Address(600, "Misty Lanes"), "Balin"));
+        listEmployee.add(new Employee(3, new Address(700, "Bramles Lane"), "Bofur"));
+        listEmployee.add(new Employee(4, new Address(800, "Bag End"), "Bilbo Baggins"));
+        listEmployee.add(new Employee(5, new Address(900, "Rivendell"), "Elrond"));
+
+        Map<Integer, Map<String, String>> employeeAddressMap1 = mUtil.createNestedMapfromStream(listEmployee);
+
+        Map<Integer, Map<Integer, Address>> employeeMap1 = mUtil.createNestedObjectMap(listEmployee);
+
+        assertNotEquals(employeeAddressMap1, actualEmployeeAddressMap);
+
+        assertNotEquals(employeeMap1, actualEmployeeMap);
+    }
+
+    @Test
+    public void whencomparingDifferentObjectValuesUsingEquals_thenFail() {
+        listEmployee.clear();
+        listEmployee.add(new Employee(1, new Address(124, "Timbuktoo"), "Thorin Oakenshield"));
+        listEmployee.add(new Employee(2, new Address(100, "Misty Lanes"), "Balin"));
+        listEmployee.add(new Employee(3, new Address(156, "Brambles Lane"), "Bofur"));
+        listEmployee.add(new Employee(4, new Address(200, "Bag End"), "Bilbo Baggins"));
+        listEmployee.add(new Employee(5, new Address(23, "Rivendell"), "Elrond"));
+
+        Map<Integer, Map<Integer, Object>> employeeMap1 = listEmployee.stream().collect(Collectors.groupingBy(
+                (Employee emp) -> emp.getEmployeeId(),
+                Collectors.toMap((Employee emp) -> emp.getAddress().getAddressId(), fEmpObj -> fEmpObj.getAddress())));
+
+        assertNotSame(employeeMap1, actualEmployeeMap);
+        assertNotEquals(employeeMap1, actualEmployeeMap);
+
+        Map<Integer, Map<Integer, Address>> expectedMap = setupAddressObjectMap();
+        assertNotSame(expectedMap, actualEmployeeMap);
+        assertNotEquals(expectedMap, actualEmployeeMap);
+
+    }
+
+    @Test
+    public void whenCompareTwoHashMapsUsingEquals_thenSuccess() {
+        Map<String, Map<Integer, String>> outerBakedGoodsMap4 = new HashMap<>();
+        outerBakedGoodsMap4.putAll(actualBakedGoodsMap);
+
+        assertEquals(actualBakedGoodsMap, outerBakedGoodsMap4);
+
+        Map<Integer, Map<Integer, Address>> employeeMap1 = new HashMap<>();
+        employeeMap1.putAll(actualEmployeeMap);
+        assertEquals(actualEmployeeMap, employeeMap1);
+    }
+
+    @Test
+    public void whenAddElementinHashMaps_thenSuccess() {
+        assertEquals(actualBakedGoodsMap.get("Cake").size(), 5);
+        actualBakedGoodsMap.get("Cake").put(6, "Cranberry");
+        assertEquals(actualBakedGoodsMap.get("Cake").size(), 6);
+    }
+
+    @Test
+    public void whenDeleteElementinHashMaps_thenSuccess() {
+        assertNotEquals(actualBakedGoodsMap.get("Cake").get(5), null);
+        actualBakedGoodsMap.get("Cake").remove(5);
+        assertEquals(actualBakedGoodsMap.get("Cake").get(5), null);
+
+        actualBakedGoodsMap.put("Eclair", new HashMap<Integer, String>() {
+            {
+                put(1, "Dark Chocolate");
+            }
+        });
+
+        assertNotEquals(actualBakedGoodsMap.get("Eclair").get(1), null);
+        actualBakedGoodsMap.get("Eclair").remove(1);
+        assertEquals(actualBakedGoodsMap.get("Eclair").get(1), null);
+
+        actualBakedGoodsMap.put("Eclair", new HashMap<Integer, String>() {
+            {
+                put(1, "Dark Chocolate");
+            }
+        });
+
+        assertNotEquals(actualBakedGoodsMap.get("Eclair"), null);
+        actualBakedGoodsMap.remove("Eclair");
+        assertEquals(actualBakedGoodsMap.get("Eclair"), null);
+    }
+
+    @Test
+    public void whenFlattenMap_thenRemovesNesting() {
+
+        Map<String, String> flattenedBakedGoodsMap = mUtil.flattenMap(actualBakedGoodsMap);
+        assertThat(flattenedBakedGoodsMap, IsMapContaining.hasKey("Donut.2"));
+
+        Map<String, String> flattenedEmployeeAddressMap = mUtil.flattenMap(actualEmployeeAddressMap);
+        assertThat(flattenedEmployeeAddressMap, IsMapContaining.hasKey("200.Bag End"));
+    }
+
+    @Before
+    public void buildMaps() {
+
+        batterList = Arrays.asList("Mulberry", "Cranberry", "Blackberry", "Mixed fruit", "Orange");
+
+        actualBakedGoodsMap.put("Cake", mUtil.buildInnerMap(batterList));
+
+        batterList = new ArrayList<>();
+        batterList = Arrays.asList("Candy", "Dark Chocolate", "Chocolate", "Jam filled", "Pineapple");
+
+        actualBakedGoodsMap.put("Donut", mUtil.buildInnerMap(batterList));
+
+        listEmployee.add(new Employee(1, new Address(124, "Timbuktoo"), "Thorin Oakenshield"));
+        listEmployee.add(new Employee(2, new Address(100, "Misty Lanes"), "Balin"));
+        listEmployee.add(new Employee(3, new Address(156, "Brambles Lane"), "Bofur"));
+        listEmployee.add(new Employee(4, new Address(200, "Bag End"), "Bilbo Baggins"));
+        listEmployee.add(new Employee(5, new Address(23, "Rivendell"), "Elrond"));
+
+        actualEmployeeAddressMap = mUtil.createNestedMapfromStream(listEmployee);
+
+        actualEmployeeMap = mUtil.createNestedObjectMap(listEmployee);
+
+    }
+
+    private Map<Integer, Map<Integer, Address>> setupAddressObjectMap() {
+
+        Map<Integer, Map<Integer, Address>> expectedMap = new HashMap<>();
+
+        expectedMap.put(1, new HashMap<Integer, Address>() {
+            {
+                put(124, new Address(124, "Timbuktoo"));
+            }
+        });
+        expectedMap.put(2, new HashMap<Integer, Address>() {
+            {
+                put(100, new Address(100, "Misty Lanes"));
+            }
+        });
+        expectedMap.put(3, new HashMap<Integer, Address>() {
+            {
+                put(156, new Address(156, "Brambles Lane"));
+            }
+        });
+        expectedMap.put(4, new HashMap<Integer, Address>() {
+            {
+                put(200, new Address(200, "Bag End"));
+            }
+        });
+        expectedMap.put(5, new HashMap<Integer, Address>() {
+            {
+                put(23, new Address(23, "Rivendell"));
+            }
+        });
+        return expectedMap;
+    }
+
+}

core-java-modules/core-java-string-algorithms-2/src/test/java/com/baeldung/isuppercase/StringFirstCharacterUppercase.java

@@ -0,0 +1,32 @@
+package com.baeldung.isuppercase;
+
+import com.google.common.base.Ascii;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestInstance;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.matchesPattern;
+
+@TestInstance(TestInstance.Lifecycle.PER_CLASS)
+public class StringFirstCharacterUppercase {
+
+    @Test
+    public void givenString_whenCheckingWithCharacterIsUpperCase_thenStringCapitalized() {
+        String example = "Katie";
+        Assertions.assertTrue(Character.isUpperCase(example.charAt(0)));
+    }
+
+    @Test
+    public void givenString_whenCheckingWithRegex_thenStringCapitalized() {
+        String example = "Katie";
+        String regEx = "[A-Z]\\w*";
+        assertThat(example, matchesPattern(regEx));
+    }
+
+    @Test
+    public void givenString_whenCheckingWithGuava_thenStringCapitalized() {
+        String example = "Katie";
+        Assertions.assertTrue(Ascii.isUpperCase(example.charAt(0)));
+    }
+}

core-java-modules/core-java-string-operations-3/src/test/java/com/baeldung/multipledelimiterssplit/MultipleDelimitersSplitUnitTest.java

@@ -17,7 +17,7 @@ public class MultipleDelimitersSplitUnitTest {
     @Test
     public void givenString_whenSplittingByMultipleDelimitersWithRegEx_thenStringSplit() {
         String example = "Mary;Thomas:Jane-Kate";
-        String[] names = example.split(";|:|-");
+        String[] names = example.split("[;:-]");
         String[] expectedNames = new String[]{"Mary", "Thomas", "Jane", "Kate"};
         Assertions.assertEquals(4, names.length);
         Assertions.assertArrayEquals(expectedNames, names);
@@ -38,7 +38,7 @@ public class MultipleDelimitersSplitUnitTest {
         String example = "Mary;Thomas:Jane-Kate";
         String[] expectedArray = new String[]{"Mary", "Thomas", "Jane", "Kate"};
         Iterable<String> expected = Arrays.asList(expectedArray);
-        Iterable<String> names = Splitter.on(Pattern.compile(";|:|-")).split(example);
+        Iterable<String> names = Splitter.on(Pattern.compile("[;:-]")).split(example);
         Assertions.assertEquals(4, Iterators.size(names.iterator()));
         Assertions.assertIterableEquals(expected, names);
     }
@@ -48,7 +48,7 @@ public class MultipleDelimitersSplitUnitTest {
         String example = "Mary;Thomas:Jane-Kate";
         String[] expectedArray = new String[]{"Mary", "Thomas", "Jane", "Kate"};
         Iterable<String> expected = Arrays.asList(expectedArray);
-        Iterable<String> names = Splitter.onPattern(";|:|-").split(example);
+        Iterable<String> names = Splitter.onPattern("[;:-]").split(example);
         Assertions.assertEquals(4, Iterators.size(names.iterator()));
         Assertions.assertIterableEquals(expected, names);
     }

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

@@ -61,6 +61,11 @@
             <artifactId>moneta</artifactId>
             <version>${javamoney.moneta.version}</version>
         </dependency>
+        <dependency>
+		    <groupId>org.springframework</groupId>
+		    <artifactId>spring-core</artifactId>
+		    <version>${spring.core.version}</version>
+        </dependency>
     </dependencies>
 
     <build>
@@ -187,6 +192,7 @@
         <maven-javadoc-plugin.version>3.0.0-M1</maven-javadoc-plugin.version>
         <source.version>1.8</source.version>
         <target.version>1.8</target.version>
+        <spring.core.version>4.3.20.RELEASE</spring.core.version>
     </properties>
 
 </project>

core-java-modules/core-java/src/main/java/com/baeldung/util/MySerializationUtils.java

@@ -0,0 +1,44 @@
+package com.baeldung.util;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.io.Serializable;
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+
+public class MySerializationUtils {
+
+    public static <T extends Serializable> byte[] serialize(T obj) throws IOException {
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        ObjectOutputStream oos = new ObjectOutputStream(baos);
+        oos.writeObject(obj);
+        oos.close();
+        return baos.toByteArray();
+    }
+
+    public static <T extends Serializable> T deserialize(byte[] b, Class<T> cl) throws IOException, ClassNotFoundException {
+        ByteArrayInputStream bais = new ByteArrayInputStream(b);
+        ObjectInputStream ois = new ObjectInputStream(bais);
+        Object o = ois.readObject();
+        return cl.cast(o);
+    }
+
+    public static boolean isSerializable(Class<?> it) {
+        boolean serializable = it.isPrimitive() || it.isInterface() || Serializable.class.isAssignableFrom(it);
+        if (!serializable) {
+            return serializable;
+        }
+        Field[] declaredFields = it.getDeclaredFields();
+        for (Field field : declaredFields) {
+            if (Modifier.isVolatile(field.getModifiers()) || Modifier.isTransient(field.getModifiers()) || Modifier.isStatic(field.getModifiers())) {
+                continue;
+            }
+            Class<?> fieldType = field.getType();
+            return isSerializable(fieldType);
+        }
+        return serializable;
+    }
+}

core-java-modules/core-java/src/test/java/com/baeldung/serialization/SerializationUnitTest.java

@@ -0,0 +1,111 @@
+package com.baeldung.serialization;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.NotSerializableException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.io.Serializable;
+
+import org.apache.commons.lang3.SerializationUtils;
+import org.junit.Test;
+
+import com.baeldung.util.MySerializationUtils;
+
+public class SerializationUnitTest {
+
+    @Test(expected = NotSerializableException.class)
+    public void whenSerializing_ThenThrowsError() throws IOException {
+        Address address = new Address();
+        address.setHouseNumber(10);
+        FileOutputStream fileOutputStream = new FileOutputStream("yofile.txt");
+        try (ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream)) {
+            objectOutputStream.writeObject(address);
+        }
+    }
+
+    @Test
+    public void whenSerializingAndDeserializing_ThenObjectIsTheSame() throws IOException, ClassNotFoundException {
+        Person p = new Person();
+        p.setAge(20);
+        p.setName("Joe");
+
+        FileOutputStream fileOutputStream = new FileOutputStream("yofile.txt");
+        try (ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream)) {
+            objectOutputStream.writeObject(p);
+        }
+
+        FileInputStream fileInputStream = new FileInputStream("yofile.txt");
+        try (ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream)) {
+            Person p2 = (Person) objectInputStream.readObject();
+            assertEquals(p2.getAge(), p.getAge());
+            assertEquals(p2.getName(), p.getName());
+        }
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void whenSerializingUsingApacheCommons_ThenThrowsError() {
+        Address address = new Address();
+        address.setHouseNumber(10);
+        SerializationUtils.serialize((Serializable) address);
+    }
+
+    @Test
+    public void whenSerializingAndDeserializingUsingApacheCommons_ThenObjectIsTheSame() {
+        Person p = new Person();
+        p.setAge(20);
+        p.setName("Joe");
+        byte[] serialize = SerializationUtils.serialize(p);
+        Person p2 = (Person) SerializationUtils.deserialize(serialize);
+        assertEquals(p2.getAge(), p.getAge());
+        assertEquals(p2.getName(), p.getName());
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void whenSerializingUsingSpringSerializationUtils_ThenThrowsError() {
+        Address address = new Address();
+        address.setHouseNumber(10);
+        org.springframework.util.SerializationUtils.serialize((Serializable) address);
+    }
+
+    @Test
+    public void whenSerializingAndDeserializingUsingSpringSerializationUtils_ThenObjectIsTheSame() {
+        Person p = new Person();
+        p.setAge(20);
+        p.setName("Joe");
+        byte[] serialize = org.springframework.util.SerializationUtils.serialize(p);
+        Person p2 = (Person) org.springframework.util.SerializationUtils.deserialize(serialize);
+        assertEquals(p2.getAge(), p.getAge());
+        assertEquals(p2.getName(), p.getName());
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void whenSerializingUsingCustomSerializationUtils_ThenThrowsError() throws IOException {
+        Address address = new Address();
+        address.setHouseNumber(10);
+        MySerializationUtils.serialize((Serializable) address);
+    }
+
+    @Test
+    public void whenSerializingAndDeserializingUsingCustomSerializationUtils_ThenObjectIsTheSame() throws IOException, ClassNotFoundException {
+        Person p = new Person();
+        p.setAge(20);
+        p.setName("Joe");
+        byte[] serialize = MySerializationUtils.serialize(p);
+        Person p2 = MySerializationUtils.deserialize(serialize, Person.class);
+        assertEquals(p2.getAge(), p.getAge());
+        assertEquals(p2.getName(), p.getName());
+    }
+
+    @Test
+    public void whenSerializingUsingCustomSerializationUtils_ThanOk() {
+        assertFalse(MySerializationUtils.isSerializable(Address.class));
+        assertTrue(MySerializationUtils.isSerializable(Person.class));
+        assertTrue(MySerializationUtils.isSerializable(Integer.class));
+    }
+}