Init commit all code

core-java-modules/core-java-8/.gitignore

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+*.class
+
+0.*
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+.resourceCache
+
+# Packaged files #
+*.jar
+*.war
+*.ear
+
+# Files generated by integration tests
+*.txt
+backup-pom.xml
+/bin/
+/temp
+
+#IntelliJ specific
+.idea/
+*.iml

core-java-modules/core-java-8/README.md

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+## Core Java 8
+
+This module contains articles about Java 8 core features
+
+### Relevant Articles: 
+- [New Features in Java 8](https://www.baeldung.com/java-8-new-features)
+- [Guide to Java 8 groupingBy Collector](https://www.baeldung.com/java-groupingby-collector)
+- [Strategy Design Pattern in Java 8](https://www.baeldung.com/java-strategy-pattern)
+- [Guide to Java 8 Comparator.comparing()](https://www.baeldung.com/java-8-comparator-comparing)
+- [Guide to the Java 8 forEach](https://www.baeldung.com/foreach-java)
+- [Introduction to Spliterator in Java](https://www.baeldung.com/java-spliterator)
+- [Finding Min/Max in an Array with Java](https://www.baeldung.com/java-array-min-max)
+- [Internationalization and Localization in Java 8](https://www.baeldung.com/java-8-localization)
+- [Generalized Target-Type Inference in Java](https://www.baeldung.com/java-generalized-target-type-inference)
+- [[More -->]](/core-java-modules/core-java-8-2)

core-java-modules/core-java-8/pom.xml

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+<?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-8</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-8</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.ossez.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.2-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>${commons-collections4.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>provided</scope>
+        </dependency>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-8</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <properties>
+        <!-- util -->
+        <commons-collections4.version>4.1</commons-collections4.version>
+        <!-- testing -->
+        <assertj.version>3.6.1</assertj.version>
+    </properties>
+
+</project>

core-java-modules/core-java-8/src/main/java/com/ossez/aspect/ChangeCallsToCurrentTimeInMillisMethod.aj

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+package com.baeldung.aspect;
+
+public aspect ChangeCallsToCurrentTimeInMillisMethod {
+    long around():
+            call(public static native long java.lang.System.currentTimeMillis())
+                    && within(user.code.base.pckg.*) {
+        return 0;
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/java_8_features/Address.java

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+package com.ossez.java_8_features;
+
+public class Address {
+
+    private String street;
+
+    public String getStreet() {
+        return street;
+    }
+
+    public void setStreet(String street) {
+        this.street = street;
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/java_8_features/CustomException.java

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+package com.ossez.java_8_features;
+
+public class CustomException extends RuntimeException {
+}

core-java-modules/core-java-8/src/main/java/com/ossez/java_8_features/OptionalAddress.java

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+package com.ossez.java_8_features;
+
+import java.util.Optional;
+
+public class OptionalAddress {
+
+    private String street;
+
+    public Optional<String> getStreet() {
+        return Optional.ofNullable(street);
+    }
+
+    public void setStreet(String street) {
+        this.street = street;
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/java_8_features/OptionalUser.java

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+package com.ossez.java_8_features;
+
+import java.util.Optional;
+
+public class OptionalUser {
+
+    private OptionalAddress address;
+
+    public Optional<OptionalAddress> getAddress() {
+        return Optional.of(address);
+    }
+
+    public void setAddress(OptionalAddress address) {
+        this.address = address;
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/java_8_features/User.java

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+package com.ossez.java_8_features;
+
+import java.util.Optional;
+
+public class User {
+
+    private String name;
+
+    private Address address;
+
+    public Address getAddress() {
+        return address;
+    }
+
+    public void setAddress(Address address) {
+        this.address = address;
+    }
+
+    public User() {
+    }
+
+    public User(String name) {
+        this.name = name;
+    }
+
+    public static boolean isRealUser(User user) {
+        return true;
+    }
+
+    public String getOrThrow() {
+        String value = null;
+        Optional<String> valueOpt = Optional.ofNullable(value);
+        String result = valueOpt.orElseThrow(CustomException::new).toUpperCase();
+        return result;
+    }
+
+    public boolean isLegalName(String name) {
+        return name.length() > 3 && name.length() < 16;
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/java_8_features/Vehicle.java

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+package com.ossez.java_8_features;
+
+public interface Vehicle {
+
+    void moveTo(long altitude, long longitude);
+
+    static String producer() {
+        return "N&F Vehicles";
+    }
+
+    default long[] startPosition() {
+        return new long[] { 23, 15 };
+    }
+
+    default String getOverview() {
+        return "ATV made by " + producer();
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/java_8_features/VehicleImpl.java

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+package com.ossez.java_8_features;
+
+public class VehicleImpl implements Vehicle {
+
+    @Override
+    public void moveTo(long altitude, long longitude) {
+        // do nothing
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/java_8_features/groupingby/BlogPost.java

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+package com.ossez.java_8_features.groupingby;
+
+public class BlogPost {
+    private String title;
+    private String author;
+    private BlogPostType type;
+    private int likes;
+
+    public BlogPost(String title, String author, BlogPostType type, int likes) {
+        this.title = title;
+        this.author = author;
+        this.type = type;
+        this.likes = likes;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public String getAuthor() {
+        return author;
+    }
+
+    public BlogPostType getType() {
+        return type;
+    }
+
+    public int getLikes() {
+        return likes;
+    }
+
+    @Override
+    public String toString() {
+        return "BlogPost{" + "title='" + title + '\'' + ", type=" + type + ", likes=" + likes + '}';
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/java_8_features/groupingby/BlogPostType.java

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+package com.ossez.java_8_features.groupingby;
+
+public enum BlogPostType {
+    NEWS, REVIEW, GUIDE
+}

core-java-modules/core-java-8/src/main/java/com/ossez/java_8_features/groupingby/Tuple.java

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+package com.ossez.java_8_features.groupingby;
+
+import java.util.Objects;
+
+public class Tuple {
+    private final BlogPostType type;
+    private final String author;
+
+    public Tuple(BlogPostType type, String author) {
+        this.type = type;
+        this.author = author;
+    }
+
+    public BlogPostType getType() {
+        return type;
+    }
+
+    public String getAuthor() {
+        return author;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+        if (o == null || getClass() != o.getClass())
+            return false;
+        Tuple tuple = (Tuple) o;
+        return type == tuple.type && author.equals(tuple.author);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(type, author);
+    }
+
+    @Override
+    public String toString() {
+        return "Tuple{" + "type=" + type + ", author='" + author + '\'' + '}';
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/nullsafecollectionstreams/NullSafeCollectionStreamsUsingCommonsEmptyIfNull.java

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+package com.ossez.nullsafecollectionstreams;
+
+import java.util.Collection;
+import java.util.stream.Stream;
+import static org.apache.commons.collections4.CollectionUtils.emptyIfNull;
+
+public class NullSafeCollectionStreamsUsingCommonsEmptyIfNull {
+
+    /**
+    * This method shows how to make a null safe stream from a collection through the use of 
+    * emptyIfNull() method from Apache Commons CollectionUtils library
+    * 
+     * @param collection The collection that is to be converted into a stream
+     * @return The stream that has been created from the collection or an empty stream if the collection is null
+    */
+    public Stream<String> collectionAsStream(Collection<String> collection) {
+        return emptyIfNull(collection).stream();
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/nullsafecollectionstreams/NullSafeCollectionStreamsUsingJava8OptionalContainer.java

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+package com.ossez.nullsafecollectionstreams;
+
+import java.util.Collection;
+import java.util.Optional;
+import java.util.stream.Stream;
+
+public class NullSafeCollectionStreamsUsingJava8OptionalContainer {
+
+    /**
+    * This method shows how to make a null safe stream from a collection  through the use of 
+    * Java SE 8’s Optional Container
+    * 
+     * @param collection The collection that is to be converted into a stream
+     * @return The stream that has been created from the collection or an empty stream if the collection is null
+    */
+    public Stream<String> collectionAsStream(Collection<String> collection) {
+        return Optional.ofNullable(collection)
+            .map(Collection::stream)
+            .orElseGet(Stream::empty);
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/nullsafecollectionstreams/NullSafeCollectionStreamsUsingNullDereferenceCheck.java

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+package com.ossez.nullsafecollectionstreams;
+
+import java.util.Collection;
+import java.util.stream.Stream;
+
+public class NullSafeCollectionStreamsUsingNullDereferenceCheck {
+    
+    /**
+    * This method shows how to make a null safe stream from a collection through the use of a check 
+    * to prevent null dereferences
+    * 
+    * @param collection The collection that is to be converted into a stream
+    * @return The stream that has been created from the collection or an empty stream if the collection is null
+    */
+    public Stream<String> collectionAsStream(Collection<String> collection) {
+        return collection == null ? Stream.empty() : collection.stream();
+    }    
+
+
+}

core-java-modules/core-java-8/src/main/java/com/ossez/spliteratorAPI/Article.java

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+package com.ossez.spliteratorAPI;
+
+import java.util.List;
+
+public class Article {
+    private List<Author> listOfAuthors;
+    private int id;
+    private String name;
+
+    public Article(String name) {
+        this.name = name;
+    }
+
+    public Article(List<Author> listOfAuthors, int id) {
+        super();
+        this.listOfAuthors = listOfAuthors;
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public List<Author> getListOfAuthors() {
+        return listOfAuthors;
+    }
+
+    public void setListOfAuthors(List<Author> listOfAuthors) {
+        this.listOfAuthors = listOfAuthors;
+    }
+
+}

core-java-modules/core-java-8/src/main/java/com/ossez/spliteratorAPI/Author.java

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+package com.ossez.spliteratorAPI;
+
+public class Author {
+    private String name;
+    private int relatedArticleId;
+
+    public Author(String name, int relatedArticleId) {
+        this.name = name;
+        this.relatedArticleId = relatedArticleId;
+    }
+
+    public int getRelatedArticleId() {
+        return relatedArticleId;
+    }
+
+    public void setRelatedArticleId(int relatedArticleId) {
+        this.relatedArticleId = relatedArticleId;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public String toString() {
+        return "[name: " + name + ", relatedId: " + relatedArticleId + "]";
+    }
+}
+

core-java-modules/core-java-8/src/main/java/com/ossez/spliteratorAPI/Executor.java

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+package com.ossez.spliteratorAPI;
+
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class Executor {
+
+	public static int countAutors(Stream<Author> stream) {
+		RelatedAuthorCounter wordCounter = stream.reduce(new RelatedAuthorCounter(0, true),
+				RelatedAuthorCounter::accumulate, RelatedAuthorCounter::combine);
+		return wordCounter.getCounter();
+	}
+
+	public static List<Article> generateElements() {
+		return Stream.generate(() -> new Article("Java")).limit(35000).collect(Collectors.toList());
+	}
+
+}

core-java-modules/core-java-8/src/main/java/com/ossez/spliteratorAPI/RelatedAuthorCounter.java

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+package com.ossez.spliteratorAPI;
+
+public class RelatedAuthorCounter {
+    private final int counter;
+    private final boolean isRelated;
+
+    public RelatedAuthorCounter(int counter, boolean isRelated) {
+        this.counter = counter;
+        this.isRelated = isRelated;
+    }
+
+    public RelatedAuthorCounter accumulate(Author author) {
+        if (author.getRelatedArticleId() == 0) {
+            return isRelated ? this : new RelatedAuthorCounter(counter, true);
+        } else {
+            return isRelated ? new RelatedAuthorCounter(counter + 1, false) : this;
+        }
+    }
+
+    public RelatedAuthorCounter combine(RelatedAuthorCounter RelatedAuthorCounter) {
+        return new RelatedAuthorCounter(counter + RelatedAuthorCounter.counter, RelatedAuthorCounter.isRelated);
+    }
+
+    public int getCounter() {
+        return counter;
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/spliteratorAPI/RelatedAuthorSpliterator.java

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+package com.ossez.spliteratorAPI;
+
+import java.util.List;
+import java.util.Spliterator;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Consumer;
+
+public class RelatedAuthorSpliterator implements Spliterator<Author> {
+	private final List<Author> list;
+	AtomicInteger current = new AtomicInteger();
+
+	public RelatedAuthorSpliterator(List<Author> list) {
+		this.list = list;
+	}
+
+	@Override
+	public boolean tryAdvance(Consumer<? super Author> action) {
+
+		action.accept(list.get(current.getAndIncrement()));
+		return current.get() < list.size();
+	}
+
+	@Override
+	public Spliterator<Author> trySplit() {
+		int currentSize = list.size() - current.get();
+		if (currentSize < 10) {
+			return null;
+		}
+		for (int splitPos = currentSize / 2 + current.intValue(); splitPos < list.size(); splitPos++) {
+			if (list.get(splitPos).getRelatedArticleId() == 0) {
+				Spliterator<Author> spliterator = new RelatedAuthorSpliterator(list.subList(current.get(), splitPos));
+				current.set(splitPos);
+				return spliterator;
+			}
+		}
+		return null;
+	}
+
+	@Override
+	public long estimateSize() {
+		return list.size() - current.get();
+	}
+
+	@Override
+	public int characteristics() {
+		return CONCURRENT;
+	}
+
+}

core-java-modules/core-java-8/src/main/java/com/ossez/spliteratorAPI/Task.java

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+package com.ossez.spliteratorAPI;
+
+import java.util.Spliterator;
+import java.util.concurrent.Callable;
+
+public class Task implements Callable<String> {
+    private Spliterator<Article> spliterator;
+    private final static String SUFFIX = "- published by Baeldung";
+
+    public Task(Spliterator<Article> spliterator) {
+        this.spliterator = spliterator;
+    }
+
+    @Override
+    public String call() {
+        int current = 0;
+        while (spliterator.tryAdvance(article -> {
+            article.setName(article.getName()
+                .concat(SUFFIX));
+        })) {
+            current++;
+        }
+        ;
+        return Thread.currentThread()
+            .getName() + ":" + current;
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/strategy/ChristmasDiscounter.java

@@ -0,0 +1,11 @@
+package com.ossez.strategy;
+
+import java.math.BigDecimal;
+
+public class ChristmasDiscounter implements Discounter {
+
+    @Override
+    public BigDecimal apply(BigDecimal amount) {
+        return amount.multiply(BigDecimal.valueOf(0.9));
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/strategy/Discounter.java

@@ -0,0 +1,23 @@
+package com.ossez.strategy;
+
+import java.math.BigDecimal;
+import java.util.function.UnaryOperator;
+
+public interface Discounter extends UnaryOperator<BigDecimal> {
+
+    default Discounter combine(Discounter after) {
+        return value -> after.apply(this.apply(value));
+    }
+
+    static Discounter christmas() {
+        return (amount) -> amount.multiply(BigDecimal.valueOf(0.9));
+    }
+
+    static Discounter newYear() {
+        return (amount) -> amount.multiply(BigDecimal.valueOf(0.8));
+    }
+
+    static Discounter easter() {
+        return (amount) -> amount.multiply(BigDecimal.valueOf(0.5));
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/strategy/EasterDiscounter.java

@@ -0,0 +1,11 @@
+package com.ossez.strategy;
+
+import java.math.BigDecimal;
+
+public class EasterDiscounter implements Discounter {
+
+    @Override
+    public BigDecimal apply(BigDecimal amount) {
+        return amount.multiply(BigDecimal.valueOf(0.5));
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/streamreduce/application/Application.java

@@ -0,0 +1,63 @@
+package com.ossez.streamreduce.application;
+
+import com.ossez.streamreduce.entities.User;
+import com.ossez.streamreduce.utilities.NumberUtils;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class Application {
+
+    public static void main(String[] args) {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        int result1 = numbers.stream().reduce(0, (a, b) -> a + b);
+        System.out.println(result1);
+        
+        int result2 = numbers.stream().reduce(0, Integer::sum);
+        System.out.println(result2);
+
+        List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
+        String result3 = letters.stream().reduce("", (a, b) -> a + b);
+        System.out.println(result3);
+        
+        String result4 = letters.stream().reduce("", String::concat);
+        System.out.println(result4);
+
+        String result5 = letters.stream().reduce("", (a, b) -> a.toUpperCase() + b.toUpperCase());
+        System.out.println(result5);
+        
+        List<User> users = Arrays.asList(new User("John", 30), new User("Julie", 35));
+        int result6 = users.stream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
+        System.out.println(result6);
+        
+        String result7 = letters.parallelStream().reduce("", String::concat);
+        System.out.println(result7);
+        
+        int result8 = users.parallelStream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
+        System.out.println(result8);
+        
+        List<User> userList = new ArrayList<>();
+        for (int i = 0; i <= 1000000; i++) {
+            userList.add(new User("John" + i, i));
+        }
+        
+        long t1 = System.currentTimeMillis();
+        int result9 = userList.stream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
+        long t2 = System.currentTimeMillis();
+        System.out.println(result9);
+        System.out.println("Sequential stream time: " + (t2 - t1) + "ms");
+        
+        long t3 = System.currentTimeMillis();
+        int result10 = userList.parallelStream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
+        long t4 = System.currentTimeMillis();
+        System.out.println(result10);
+        System.out.println("Parallel stream time: " + (t4 - t3) + "ms");
+        
+        int result11 = NumberUtils.divideListElements(numbers, 1);
+        System.out.println(result11);
+        
+        int result12 = NumberUtils.divideListElementsWithExtractedTryCatchBlock(numbers, 0);
+        System.out.println(result12);
+    }    
+}

core-java-modules/core-java-8/src/main/java/com/ossez/streamreduce/entities/Rating.java

@@ -0,0 +1,39 @@
+package com.ossez.streamreduce.entities;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Rating {
+
+    double points;
+    List<Review> reviews = new ArrayList<>();
+
+    public Rating() {}
+
+    public void add(Review review) {
+        reviews.add(review);
+        computeRating();
+    }
+
+    private double computeRating() {
+        double totalPoints = reviews.stream().map(Review::getPoints).reduce(0, Integer::sum);
+        this.points = totalPoints / reviews.size();
+        return this.points;
+    }
+
+    public static Rating average(Rating r1, Rating r2) {
+        Rating combined = new Rating();
+        combined.reviews = new ArrayList<>(r1.reviews);
+        combined.reviews.addAll(r2.reviews);
+        combined.computeRating();
+        return combined;
+    }
+
+    public double getPoints() {
+        return points;
+    }
+
+    public List<Review> getReviews() {
+        return reviews;
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/streamreduce/entities/Review.java

@@ -0,0 +1,28 @@
+package com.ossez.streamreduce.entities;
+
+public class Review {
+
+    int points;
+    String review;
+
+    public Review(int points, String review) {
+        this.points = points;
+        this.review = review;
+    }
+
+    public int getPoints() {
+        return points;
+    }
+
+    public void setPoints(int points) {
+        this.points = points;
+    }
+
+    public String getReview() {
+        return review;
+    }
+
+    public void setReview(String review) {
+        this.review = review;
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/streamreduce/entities/User.java

@@ -0,0 +1,30 @@
+package com.ossez.streamreduce.entities;
+
+public class User {
+
+    private final String name;
+    private final int age;
+    private final Rating rating = new Rating();
+
+    public User(String name, int age) {
+        this.name = name;
+        this.age = age;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public Rating getRating() {
+        return rating;
+    }
+
+    @Override
+    public String toString() {
+        return "User{" + "name=" + name + ", age=" + age + '}';
+    }
+}

core-java-modules/core-java-8/src/main/java/com/ossez/streamreduce/utilities/NumberUtils.java

@@ -0,0 +1,52 @@
+package com.ossez.streamreduce.utilities;
+
+import java.util.List;
+import java.util.function.BiFunction;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public abstract class NumberUtils {
+
+    private static final Logger LOGGER = Logger.getLogger(NumberUtils.class.getName());
+
+    public static int divideListElements(List<Integer> values, Integer divider) {
+        return values.stream()
+                .reduce(0, (a, b) -> {
+                    try {
+                        return a / divider + b / divider;
+                    } catch (ArithmeticException e) {
+                        LOGGER.log(Level.INFO, "Arithmetic Exception: Division by Zero");
+                    }
+                    return 0;
+                });
+    }
+    
+    public static int divideListElementsWithExtractedTryCatchBlock(List<Integer> values, int divider) {
+        return values.stream().reduce(0, (a, b) -> divide(a, divider) + divide(b, divider));
+    }
+    
+    public static int divideListElementsWithApplyFunctionMethod(List<Integer> values, int divider) {
+        BiFunction<Integer, Integer, Integer> division = (a, b) -> a / b;
+        return values.stream().reduce(0, (a, b) -> applyFunction(division, a, divider) + applyFunction(division, b, divider));
+    }
+    
+    private static int divide(int value, int factor) {
+        int result = 0;
+        try {
+            result = value / factor;
+        } catch (ArithmeticException e) {
+            LOGGER.log(Level.INFO, "Arithmetic Exception: Division by Zero");
+        }
+        return result;
+    }
+    
+    private static int applyFunction(BiFunction<Integer, Integer, Integer> function, int a, int b) {
+        try {
+            return function.apply(a, b);
+        }
+        catch(Exception e) {
+            LOGGER.log(Level.INFO, "Exception occurred!");
+        }
+        return 0;
+    }
+}

core-java-modules/core-java-8/src/main/resources/logback.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS}  [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="TRACE">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

core-java-modules/core-java-8/src/test/java/com/ossez/internationalization/DateFormatUnitTest.java

@@ -0,0 +1,110 @@
+package com.ossez.internationalization;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.text.DateFormat;
+import java.text.DateFormatSymbols;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.GregorianCalendar;
+import java.util.Locale;
+import java.util.TimeZone;
+
+public class DateFormatUnitTest {
+
+    @Test
+    public void givenGregorianCalendar_whenLocaleSpecificDateInstance_givenLanguageSpecificMonths() {
+        GregorianCalendar gregorianCalendar = new GregorianCalendar(2018, 1, 1, 10, 15, 20);
+        Date date = gregorianCalendar.getTime();
+
+        DateFormat itInstance = DateFormat.getDateInstance(DateFormat.FULL, Locale.ITALY);
+        DateFormat usInstance = DateFormat.getDateInstance(DateFormat.FULL, Locale.US);
+
+        Assert.assertEquals("giovedì 1 febbraio 2018", itInstance.format(date));
+        Assert.assertEquals("Thursday, February 1, 2018", usInstance.format(date));
+    }
+
+    @Test
+    public void givenGregorianCalendar_whenDateInstanceWithDifferentFormats_givenSpecificDateFormatting() {
+        GregorianCalendar gregorianCalendar = new GregorianCalendar(2018, 1, 1, 10, 15, 20);
+        Date date = gregorianCalendar.getTime();
+
+        DateFormat fullInstance = DateFormat.getDateInstance(DateFormat.FULL, Locale.ITALY);
+        DateFormat mediumInstance = DateFormat.getDateInstance(DateFormat.MEDIUM, Locale.ITALY);
+
+        Assert.assertEquals("giovedì 1 febbraio 2018", fullInstance.format(date));
+        Assert.assertEquals("1-feb-2018", mediumInstance.format(date));
+    }
+
+    @Test
+    public void givenGregorianCalendar_whenTimeInstanceWithDifferentFormats_givenSpecificTimeFormatting() {
+        GregorianCalendar gregorianCalendar = new GregorianCalendar(2018, 1, 1, 10, 15, 20);
+        gregorianCalendar.setTimeZone(TimeZone.getTimeZone("CET"));
+        TimeZone.setDefault(TimeZone.getTimeZone("CET"));
+        Date date = gregorianCalendar.getTime();
+
+        DateFormat fullInstance = DateFormat.getTimeInstance(DateFormat.FULL, Locale.ITALY);
+        DateFormat mediumInstance = DateFormat.getTimeInstance(DateFormat.MEDIUM, Locale.ITALY);
+
+        Assert.assertEquals("10.15.20 CET", fullInstance.format(date));
+        Assert.assertEquals("10.15.20" , mediumInstance.format(date));
+    }
+
+    @Test
+    public void givenGregorianCalendar_whenDateTimeInstanceWithDifferentFormats_givenSpecificDateTimeFormatting() {
+        GregorianCalendar gregorianCalendar = new GregorianCalendar(2018, 1, 1, 10, 15, 20);
+        gregorianCalendar.setTimeZone(TimeZone.getTimeZone("CET"));
+        TimeZone.setDefault(TimeZone.getTimeZone("CET"));
+        Date date = gregorianCalendar.getTime();
+
+        DateFormat ffInstance = DateFormat.getDateTimeInstance(DateFormat.FULL, DateFormat.FULL, Locale.ITALY);
+        DateFormat smInstance = DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.MEDIUM, Locale.ITALY);
+
+        Assert.assertEquals("giovedì 1 febbraio 2018 10.15.20 CET", ffInstance.format(date));
+        Assert.assertEquals("01/02/18 10.15.20", smInstance.format(date));
+    }
+
+    @Test
+    public void givenGregorianCalendar_whenLocaleSpecificDateTimeInstance_givenLocaleSpecificFormatting() {
+        GregorianCalendar gregorianCalendar = new GregorianCalendar(2018, 1, 1, 10, 15, 20);
+        gregorianCalendar.setTimeZone(TimeZone.getTimeZone("CET"));
+        TimeZone.setDefault(TimeZone.getTimeZone("CET"));
+        Date date = gregorianCalendar.getTime();
+
+        DateFormat itInstance = DateFormat.getDateTimeInstance(DateFormat.FULL, DateFormat.FULL, Locale.ITALY);
+        DateFormat jpInstance = DateFormat.getDateTimeInstance(DateFormat.FULL, DateFormat.FULL, Locale.JAPAN);
+
+        Assert.assertEquals("giovedì 1 febbraio 2018 10.15.20 CET", itInstance.format(date));
+        Assert.assertEquals("2018年2月1日 10時15分20秒 CET", jpInstance.format(date));
+    }
+
+    @Test
+    public void givenGregorianCalendar_whenCustomizedSimpleDateFormat_thenSpecificMonthRepresentations() {
+        GregorianCalendar gregorianCalendar = new GregorianCalendar(2018, 1, 1, 10, 15, 20);
+        Date date = gregorianCalendar.getTime();
+        Locale.setDefault(new Locale("pl", "PL"));
+
+        SimpleDateFormat fullMonthDateFormat = new SimpleDateFormat("dd-MMMM-yyyy HH:mm:ss:SSS");
+        SimpleDateFormat shortMonthsimpleDateFormat = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss:SSS");
+
+        Assert.assertEquals("01-lutego-2018 10:15:20:000", fullMonthDateFormat.format(date));
+        Assert.assertEquals("01-02-2018 10:15:20:000" , shortMonthsimpleDateFormat.format(date));
+    }
+
+    @Test
+    public void givenGregorianCalendar_whenCustomizedDateFormatSymbols_thenChangedDayNames() {
+        GregorianCalendar gregorianCalendar = new GregorianCalendar(2018, 1, 1, 10, 15, 20);
+        Date date = gregorianCalendar.getTime();
+        Locale.setDefault(new Locale("pl", "PL"));
+
+        DateFormatSymbols dateFormatSymbols = new DateFormatSymbols();
+        dateFormatSymbols.setWeekdays(new String[]{"A", "B", "C", "D", "E", "F", "G", "H"});
+        SimpleDateFormat standardDateFormat = new SimpleDateFormat("EEEE-MMMM-yyyy HH:mm:ss:SSS");
+        SimpleDateFormat newDaysDateFormat = new SimpleDateFormat("EEEE-MMMM-yyyy HH:mm:ss:SSS", dateFormatSymbols);
+
+        Assert.assertEquals("czwartek-lutego-2018 10:15:20:000", standardDateFormat.format(date));
+        Assert.assertEquals("F-lutego-2018 10:15:20:000", newDaysDateFormat.format(date));
+    }
+
+}

core-java-modules/core-java-8/src/test/java/com/ossez/internationalization/NumbersCurrenciesFormattingUnitTest.java

@@ -0,0 +1,76 @@
+package com.ossez.internationalization;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.math.BigDecimal;
+import java.text.DecimalFormat;
+import java.text.DecimalFormatSymbols;
+import java.text.NumberFormat;
+import java.util.Currency;
+import java.util.Locale;
+
+public class NumbersCurrenciesFormattingUnitTest {
+
+    @Test
+    public void givenDifferentLocalesAndDoubleNumber_whenNumberInstance_thenDifferentOutput() {
+        Locale usLocale = Locale.US;
+        Locale plLocale = new Locale("pl", "PL");
+        Locale deLocale = Locale.GERMANY;
+        double number = 102_300.456d;
+
+        NumberFormat usNumberFormat = NumberFormat.getInstance(usLocale);
+        NumberFormat plNumberFormat = NumberFormat.getInstance(plLocale);
+        NumberFormat deNumberFormat = NumberFormat.getInstance(deLocale);
+
+        Assert.assertEquals(usNumberFormat.format(number), "102,300.456");
+        Assert.assertEquals(plNumberFormat.format(number), "102 300,456");
+        Assert.assertEquals(deNumberFormat.format(number), "102.300,456");
+    }
+
+    @Test
+    public void givenDifferentLocalesAndDoubleAmount_whenCurrencyInstance_thenDifferentOutput() {
+        Locale usLocale = Locale.US;
+        Locale plLocale = new Locale("pl", "PL");
+        Locale deLocale = Locale.GERMANY;
+        BigDecimal number = new BigDecimal(102_300.456d);
+
+        NumberFormat usNumberFormat = NumberFormat.getCurrencyInstance(usLocale);
+        NumberFormat plNumberFormat = NumberFormat.getCurrencyInstance(plLocale);
+        NumberFormat deNumberFormat = NumberFormat.getCurrencyInstance(deLocale);
+
+        Assert.assertEquals(usNumberFormat.format(number), "$102,300.46");
+        Assert.assertEquals(plNumberFormat.format(number), "102 300,46 zł");
+        Assert.assertEquals(deNumberFormat.format(number), "102.300,46 €");
+    }
+
+    @Test
+    public void givenLocaleAndNumber_whenSpecificDecimalFormat_thenSpecificOutput() {
+        Locale.setDefault(Locale.FRANCE);
+        BigDecimal number = new BigDecimal(102_300.456d);
+
+        DecimalFormat zeroDecimalFormat = new DecimalFormat("000000000.0000");
+        DecimalFormat hashDecimalFormat = new DecimalFormat("###,###.#");
+        DecimalFormat dollarDecimalFormat = new DecimalFormat("$###,###.##");
+
+        Assert.assertEquals(zeroDecimalFormat.format(number), "000102300,4560");
+        Assert.assertEquals(hashDecimalFormat.format(number), "102 300,5");
+        Assert.assertEquals(dollarDecimalFormat.format(number), "$102 300,46");
+    }
+
+    @Test
+    public void givenLocaleAndNumber_whenSpecificDecimalFormatSymbols_thenSpecificOutput() {
+        Locale.setDefault(Locale.FRANCE);
+        BigDecimal number = new BigDecimal(102_300.456d);
+
+        DecimalFormatSymbols decimalFormatSymbols = DecimalFormatSymbols.getInstance();
+        decimalFormatSymbols.setGroupingSeparator('^');
+        decimalFormatSymbols.setDecimalSeparator('@');
+        DecimalFormat separatorsDecimalFormat = new DecimalFormat("$###,###.##");
+        separatorsDecimalFormat.setGroupingSize(4);
+        separatorsDecimalFormat.setCurrency(Currency.getInstance(Locale.JAPAN));
+        separatorsDecimalFormat.setDecimalFormatSymbols(decimalFormatSymbols);
+
+        Assert.assertEquals(separatorsDecimalFormat.format(number), "$10^2300@46");
+    }
+}

core-java-modules/core-java-8/src/test/java/com/ossez/java8/Java8DefaultStaticIntefaceMethodsUnitTest.java

@@ -0,0 +1,27 @@
+package com.ossez.java8;
+
+import com.ossez.java_8_features.Vehicle;
+import com.ossez.java_8_features.VehicleImpl;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class Java8DefaultStaticIntefaceMethodsUnitTest {
+
+    @Test
+    public void callStaticInterfaceMethdosMethods_whenExpectedResults_thenCorrect() {
+        Vehicle vehicle = new VehicleImpl();
+        String overview = vehicle.getOverview();
+        long[] startPosition = vehicle.startPosition();
+
+        assertEquals(overview, "ATV made by N&F Vehicles");
+        assertEquals(startPosition[0], 23);
+        assertEquals(startPosition[1], 15);
+    }
+
+    @Test
+    public void callDefaultInterfaceMethods_whenExpectedResults_thenCorrect() {
+        String producer = Vehicle.producer();
+        assertEquals(producer, "N&F Vehicles");
+    }
+}

core-java-modules/core-java-8/src/test/java/com/ossez/java8/Java8MethodReferenceUnitTest.java

@@ -0,0 +1,67 @@
+package com.ossez.java8;
+
+import com.ossez.java_8_features.User;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public class Java8MethodReferenceUnitTest {
+
+    private List<String> list;
+
+    @Before
+    public void init() {
+        list = new ArrayList<>();
+        list.add("One");
+        list.add("OneAndOnly");
+        list.add("Derek");
+        list.add("Change");
+        list.add("factory");
+        list.add("justBefore");
+        list.add("Italy");
+        list.add("Italy");
+        list.add("Thursday");
+        list.add("");
+        list.add("");
+    }
+
+    @Test
+    public void checkStaticMethodReferences_whenWork_thenCorrect() {
+
+        List<User> users = new ArrayList<>();
+        users.add(new User());
+        users.add(new User());
+        boolean isReal = users.stream().anyMatch(u -> User.isRealUser(u));
+        boolean isRealRef = users.stream().anyMatch(User::isRealUser);
+        assertTrue(isReal);
+        assertTrue(isRealRef);
+    }
+
+    @Test
+    public void checkInstanceMethodReferences_whenWork_thenCorrect() {
+        User user = new User();
+        boolean isLegalName = list.stream().anyMatch(user::isLegalName);
+        assertTrue(isLegalName);
+    }
+
+    @Test
+    public void checkParticularTypeReferences_whenWork_thenCorrect() {
+        long count = list.stream().filter(String::isEmpty).count();
+        assertEquals(count, 2);
+    }
+
+    @Test
+    public void checkConstructorReferences_whenWork_thenCorrect() {
+        Stream<User> stream = list.stream().map(User::new);
+        List<User> userList = stream.collect(Collectors.toList());
+        assertEquals(userList.size(), list.size());
+        assertTrue(userList.get(0) instanceof User);
+    }
+}

core-java-modules/core-java-8/src/test/java/com/ossez/java8/Java8OptionalUnitTest.java

@@ -0,0 +1,116 @@
+package com.ossez.java8;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import com.ossez.java_8_features.Address;
+import com.ossez.java_8_features.CustomException;
+import com.ossez.java_8_features.OptionalAddress;
+import com.ossez.java_8_features.OptionalUser;
+import com.ossez.java_8_features.User;
+
+public class Java8OptionalUnitTest {
+
+    private List<String> list;
+
+    @Before
+    public void init() {
+        list = new ArrayList<>();
+        list.add("One");
+        list.add("OneAndOnly");
+        list.add("Derek");
+        list.add("Change");
+        list.add("factory");
+        list.add("justBefore");
+        list.add("Italy");
+        list.add("Italy");
+        list.add("Thursday");
+        list.add("");
+        list.add("");
+    }
+
+    @Test
+    public void checkOptional_whenAsExpected_thenCorrect() {
+        Optional<String> optionalEmpty = Optional.empty();
+        assertFalse(optionalEmpty.isPresent());
+
+        String str = "value";
+        Optional<String> optional = Optional.of(str);
+        assertEquals(optional.get(), "value");
+
+        Optional<String> optionalNullable = Optional.ofNullable(str);
+        Optional<String> optionalNull = Optional.ofNullable(null);
+        assertEquals(optionalNullable.get(), "value");
+        assertFalse(optionalNull.isPresent());
+
+        List<String> listOpt = Optional.of(list).orElse(new ArrayList<>());
+        List<String> listNull = null;
+        List<String> listOptNull = Optional.ofNullable(listNull).orElse(new ArrayList<>());
+        assertTrue(listOpt == list);
+        assertTrue(listOptNull.isEmpty());
+
+        Optional<User> user = Optional.ofNullable(getUser());
+        String result = user.map(User::getAddress).map(Address::getStreet).orElse("not specified");
+        assertEquals(result, "1st Avenue");
+
+        Optional<OptionalUser> optionalUser = Optional.ofNullable(getOptionalUser());
+        String resultOpt = optionalUser.flatMap(OptionalUser::getAddress).flatMap(OptionalAddress::getStreet).orElse("not specified");
+        assertEquals(resultOpt, "1st Avenue");
+
+        Optional<User> userNull = Optional.ofNullable(getUserNull());
+        String resultNull = userNull.map(User::getAddress).map(Address::getStreet).orElse("not specified");
+        assertEquals(resultNull, "not specified");
+
+        Optional<OptionalUser> optionalUserNull = Optional.ofNullable(getOptionalUserNull());
+        String resultOptNull = optionalUserNull.flatMap(OptionalUser::getAddress).flatMap(OptionalAddress::getStreet).orElse("not specified");
+        assertEquals(resultOptNull, "not specified");
+
+    }
+
+    @Test(expected = CustomException.class)
+    public void callMethod_whenCustomException_thenCorrect() {
+        User user = new User();
+        String result = user.getOrThrow();
+    }
+
+    private User getUser() {
+        User user = new User();
+        Address address = new Address();
+        address.setStreet("1st Avenue");
+        user.setAddress(address);
+        return user;
+    }
+
+    private OptionalUser getOptionalUser() {
+        OptionalUser user = new OptionalUser();
+        OptionalAddress address = new OptionalAddress();
+        address.setStreet("1st Avenue");
+        user.setAddress(address);
+        return user;
+    }
+
+    private OptionalUser getOptionalUserNull() {
+        OptionalUser user = new OptionalUser();
+        OptionalAddress address = new OptionalAddress();
+        address.setStreet(null);
+        user.setAddress(address);
+        return user;
+    }
+
+    private User getUserNull() {
+        User user = new User();
+        Address address = new Address();
+        address.setStreet(null);
+        user.setAddress(address);
+        return user;
+    }
+
+}

core-java-modules/core-java-8/src/test/java/com/ossez/java8/comparator/Employee.java

@@ -0,0 +1,22 @@
+package com.ossez.java8.comparator;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.EqualsAndHashCode;
+import lombok.ToString;
+
+@Data
+@AllArgsConstructor
+@ToString
+@EqualsAndHashCode
+public class Employee implements Comparable<Employee>{
+    String name;
+    int age;
+    double salary;
+    long mobile;
+    
+    @Override
+    public int compareTo(Employee argEmployee) {
+        return name.compareTo(argEmployee.getName());
+    }
+    
+}

core-java-modules/core-java-8/src/test/java/com/ossez/java8/comparator/Java8ComparatorUnitTest.java

@@ -0,0 +1,152 @@
+package com.ossez.java8.comparator;
+
+import java.util.Arrays;
+import java.util.Comparator;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertTrue;
+
+public class Java8ComparatorUnitTest {
+
+    private Employee[] employees;
+    private Employee[] employeesArrayWithNulls;
+    private Employee[] sortedEmployeesByName;
+    private Employee[] sortedEmployeesByNameDesc;
+    private Employee[] sortedEmployeesByAge;
+    private Employee[] sortedEmployeesByMobile;
+    private Employee[] sortedEmployeesBySalary;
+    private Employee[] sortedEmployeesArray_WithNullsFirst;
+    private Employee[] sortedEmployeesArray_WithNullsLast;
+    private Employee[] sortedEmployeesByNameAge;
+    private Employee[] someMoreEmployees;
+    private Employee[] sortedEmployeesByAgeName;;
+
+    @Before
+    public void initData() {
+        employees = new Employee[] { new Employee("John", 25, 3000, 9922001), new Employee("Ace", 22, 2000, 5924001), new Employee("Keith", 35, 4000, 3924401) };
+        employeesArrayWithNulls = new Employee[] { new Employee("John", 25, 3000, 9922001), null, new Employee("Ace", 22, 2000, 5924001), null, new Employee("Keith", 35, 4000, 3924401) };
+
+        sortedEmployeesByName = new Employee[] { new Employee("Ace", 22, 2000, 5924001), new Employee("John", 25, 3000, 9922001), new Employee("Keith", 35, 4000, 3924401) };
+        sortedEmployeesByNameDesc = new Employee[] { new Employee("Keith", 35, 4000, 3924401), new Employee("John", 25, 3000, 9922001), new Employee("Ace", 22, 2000, 5924001) };
+
+        sortedEmployeesByAge = new Employee[] { new Employee("Ace", 22, 2000, 5924001), new Employee("John", 25, 3000, 9922001), new Employee("Keith", 35, 4000, 3924401) };
+
+        sortedEmployeesByMobile = new Employee[] { new Employee("Keith", 35, 4000, 3924401), new Employee("Ace", 22, 2000, 5924001), new Employee("John", 25, 3000, 9922001), };
+
+        sortedEmployeesBySalary = new Employee[] { new Employee("Ace", 22, 2000, 5924001), new Employee("John", 25, 3000, 9922001), new Employee("Keith", 35, 4000, 3924401), };
+
+        sortedEmployeesArray_WithNullsFirst = new Employee[] { null, null, new Employee("Ace", 22, 2000, 5924001), new Employee("John", 25, 3000, 9922001), new Employee("Keith", 35, 4000, 3924401) };
+        sortedEmployeesArray_WithNullsLast = new Employee[] { new Employee("Ace", 22, 2000, 5924001), new Employee("John", 25, 3000, 9922001), new Employee("Keith", 35, 4000, 3924401), null, null };
+
+        someMoreEmployees = new Employee[] { new Employee("Jake", 25, 3000, 9922001), new Employee("Jake", 22, 2000, 5924001), new Employee("Ace", 22, 3000, 6423001), new Employee("Keith", 35, 4000, 3924401) };
+
+        sortedEmployeesByAgeName = new Employee[] { new Employee("Ace", 22, 3000, 6423001), new Employee("Jake", 22, 2000, 5924001), new Employee("Jake", 25, 3000, 9922001), new Employee("Keith", 35, 4000, 3924401) };
+        sortedEmployeesByNameAge = new Employee[] { new Employee("Ace", 22, 3000, 6423001), new Employee("Jake", 22, 2000, 5924001), new Employee("Jake", 25, 3000, 9922001), new Employee("Keith", 35, 4000, 3924401) };
+    }
+
+    @Test
+    public void whenComparing_thenSortedByName() {
+        Comparator<Employee> employeeNameComparator = Comparator.comparing(Employee::getName);
+        Arrays.sort(employees, employeeNameComparator);
+        // System.out.println(Arrays.toString(employees));
+        assertTrue(Arrays.equals(employees, sortedEmployeesByName));
+    }
+
+    @Test
+    public void whenComparingWithComparator_thenSortedByNameDesc() {
+        Comparator<Employee> employeeNameComparator = Comparator.comparing(Employee::getName, (s1, s2) -> {
+            return s2.compareTo(s1);
+        });
+        Arrays.sort(employees, employeeNameComparator);
+        // System.out.println(Arrays.toString(employees));
+        assertTrue(Arrays.equals(employees, sortedEmployeesByNameDesc));
+    }
+
+    @Test
+    public void whenReversed_thenSortedByNameDesc() {
+        Comparator<Employee> employeeNameComparator = Comparator.comparing(Employee::getName);
+        Comparator<Employee> employeeNameComparatorReversed = employeeNameComparator.reversed();
+        Arrays.sort(employees, employeeNameComparatorReversed);
+        // System.out.println(Arrays.toString(employees));
+        assertTrue(Arrays.equals(employees, sortedEmployeesByNameDesc));
+    }
+
+    @Test
+    public void whenComparingInt_thenSortedByAge() {
+        Comparator<Employee> employeeAgeComparator = Comparator.comparingInt(Employee::getAge);
+        Arrays.sort(employees, employeeAgeComparator);
+        // System.out.println(Arrays.toString(employees));
+        assertTrue(Arrays.equals(employees, sortedEmployeesByAge));
+    }
+
+    @Test
+    public void whenComparingLong_thenSortedByMobile() {
+        Comparator<Employee> employeeMobileComparator = Comparator.comparingLong(Employee::getMobile);
+        Arrays.sort(employees, employeeMobileComparator);
+        // System.out.println(Arrays.toString(employees));
+        assertTrue(Arrays.equals(employees, sortedEmployeesByMobile));
+    }
+
+    @Test
+    public void whenComparingDouble_thenSortedBySalary() {
+        Comparator<Employee> employeeSalaryComparator = Comparator.comparingDouble(Employee::getSalary);
+        Arrays.sort(employees, employeeSalaryComparator);
+        // System.out.println(Arrays.toString(employees));
+        assertTrue(Arrays.equals(employees, sortedEmployeesBySalary));
+    }
+
+    @Test
+    public void whenNaturalOrder_thenSortedByName() {
+        Comparator<Employee> employeeNameComparator = Comparator.<Employee> naturalOrder();
+        Arrays.sort(employees, employeeNameComparator);
+        // System.out.println(Arrays.toString(employees));
+        assertTrue(Arrays.equals(employees, sortedEmployeesByName));
+    }
+
+    @Test
+    public void whenReverseOrder_thenSortedByNameDesc() {
+        Comparator<Employee> employeeNameComparator = Comparator.<Employee> reverseOrder();
+        Arrays.sort(employees, employeeNameComparator);
+        // System.out.println(Arrays.toString(employees));
+        assertTrue(Arrays.equals(employees, sortedEmployeesByNameDesc));
+    }
+
+    @Test
+    public void whenNullsFirst_thenSortedByNameWithNullsFirst() {
+        Comparator<Employee> employeeNameComparator = Comparator.comparing(Employee::getName);
+        Comparator<Employee> employeeNameComparator_nullFirst = Comparator.nullsFirst(employeeNameComparator);
+        Arrays.sort(employeesArrayWithNulls, employeeNameComparator_nullFirst);
+        // System.out.println(Arrays.toString(employeesArrayWithNulls));
+        assertTrue(Arrays.equals(employeesArrayWithNulls, sortedEmployeesArray_WithNullsFirst));
+    }
+
+    @Test
+    public void whenNullsLast_thenSortedByNameWithNullsLast() {
+        Comparator<Employee> employeeNameComparator = Comparator.comparing(Employee::getName);
+        Comparator<Employee> employeeNameComparator_nullLast = Comparator.nullsLast(employeeNameComparator);
+        Arrays.sort(employeesArrayWithNulls, employeeNameComparator_nullLast);
+        // System.out.println(Arrays.toString(employeesArrayWithNulls));
+        assertTrue(Arrays.equals(employeesArrayWithNulls, sortedEmployeesArray_WithNullsLast));
+    }
+
+    @Test
+    public void whenThenComparing_thenSortedByAgeName() {
+        Comparator<Employee> employee_Age_Name_Comparator = Comparator.comparing(Employee::getAge).thenComparing(Employee::getName);
+
+        Arrays.sort(someMoreEmployees, employee_Age_Name_Comparator);
+        // System.out.println(Arrays.toString(someMoreEmployees));
+        assertTrue(Arrays.equals(someMoreEmployees, sortedEmployeesByAgeName));
+    }
+
+    @Test
+    public void whenThenComparing_thenSortedByNameAge() {
+        Comparator<Employee> employee_Name_Age_Comparator = Comparator.comparing(Employee::getName).thenComparingInt(Employee::getAge);
+
+        Arrays.sort(someMoreEmployees, employee_Name_Age_Comparator);
+        // System.out.println(Arrays.toString(someMoreEmployees));
+        assertTrue(Arrays.equals(someMoreEmployees, sortedEmployeesByNameAge));
+    }
+
+}

core-java-modules/core-java-8/src/test/java/com/ossez/java_8_features/groupingby/Java8GroupingByCollectorUnitTest.java

@@ -0,0 +1,215 @@
+package com.ossez.java_8_features.groupingby;
+
+import static java.util.Comparator.comparingInt;
+import static java.util.stream.Collectors.averagingInt;
+import static java.util.stream.Collectors.counting;
+import static java.util.stream.Collectors.groupingBy;
+import static java.util.stream.Collectors.groupingByConcurrent;
+import static java.util.stream.Collectors.joining;
+import static java.util.stream.Collectors.mapping;
+import static java.util.stream.Collectors.maxBy;
+import static java.util.stream.Collectors.summarizingInt;
+import static java.util.stream.Collectors.summingInt;
+import static java.util.stream.Collectors.toList;
+import static java.util.stream.Collectors.toSet;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+import java.util.Arrays;
+import java.util.EnumMap;
+import java.util.IntSummaryStatistics;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.ConcurrentMap;
+
+import org.junit.Test;
+
+public class Java8GroupingByCollectorUnitTest {
+
+    private static final List<BlogPost> posts = Arrays.asList(new BlogPost("News item 1", "Author 1", BlogPostType.NEWS, 15), new BlogPost("Tech review 1", "Author 2", BlogPostType.REVIEW, 5),
+        new BlogPost("Programming guide", "Author 1", BlogPostType.GUIDE, 20), new BlogPost("News item 2", "Author 2", BlogPostType.NEWS, 35), new BlogPost("Tech review 2", "Author 1", BlogPostType.REVIEW, 15));
+
+    @Test
+    public void givenAListOfPosts_whenGroupedByType_thenGetAMapBetweenTypeAndPosts() {
+        Map<BlogPostType, List<BlogPost>> postsPerType = posts.stream()
+            .collect(groupingBy(BlogPost::getType));
+
+        assertEquals(2, postsPerType.get(BlogPostType.NEWS)
+            .size());
+        assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
+            .size());
+        assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
+            .size());
+    }
+
+    @Test
+    public void givenAListOfPosts_whenGroupedByTypeAndTheirTitlesAreJoinedInAString_thenGetAMapBetweenTypeAndCsvTitles() {
+        Map<BlogPostType, String> postsPerType = posts.stream()
+            .collect(groupingBy(BlogPost::getType, mapping(BlogPost::getTitle, joining(", ", "Post titles: [", "]"))));
+
+        assertEquals("Post titles: [News item 1, News item 2]", postsPerType.get(BlogPostType.NEWS));
+        assertEquals("Post titles: [Programming guide]", postsPerType.get(BlogPostType.GUIDE));
+        assertEquals("Post titles: [Tech review 1, Tech review 2]", postsPerType.get(BlogPostType.REVIEW));
+    }
+
+    @Test
+    public void givenAListOfPosts_whenGroupedByTypeAndSumTheLikes_thenGetAMapBetweenTypeAndPostLikes() {
+        Map<BlogPostType, Integer> likesPerType = posts.stream()
+            .collect(groupingBy(BlogPost::getType, summingInt(BlogPost::getLikes)));
+
+        assertEquals(50, likesPerType.get(BlogPostType.NEWS)
+            .intValue());
+        assertEquals(20, likesPerType.get(BlogPostType.REVIEW)
+            .intValue());
+        assertEquals(20, likesPerType.get(BlogPostType.GUIDE)
+            .intValue());
+    }
+
+    @Test
+    public void givenAListOfPosts_whenGroupedByTypeInAnEnumMap_thenGetAnEnumMapBetweenTypeAndPosts() {
+        EnumMap<BlogPostType, List<BlogPost>> postsPerType = posts.stream()
+            .collect(groupingBy(BlogPost::getType, () -> new EnumMap<>(BlogPostType.class), toList()));
+
+        assertEquals(2, postsPerType.get(BlogPostType.NEWS)
+            .size());
+        assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
+            .size());
+        assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
+            .size());
+    }
+
+    @Test
+    public void givenAListOfPosts_whenGroupedByTypeInSets_thenGetAMapBetweenTypesAndSetsOfPosts() {
+        Map<BlogPostType, Set<BlogPost>> postsPerType = posts.stream()
+            .collect(groupingBy(BlogPost::getType, toSet()));
+
+        assertEquals(2, postsPerType.get(BlogPostType.NEWS)
+            .size());
+        assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
+            .size());
+        assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
+            .size());
+    }
+
+    @Test
+    public void givenAListOfPosts_whenGroupedByTypeConcurrently_thenGetAMapBetweenTypeAndPosts() {
+        ConcurrentMap<BlogPostType, List<BlogPost>> postsPerType = posts.parallelStream()
+            .collect(groupingByConcurrent(BlogPost::getType));
+
+        assertEquals(2, postsPerType.get(BlogPostType.NEWS)
+            .size());
+        assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
+            .size());
+        assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
+            .size());
+    }
+
+    @Test
+    public void givenAListOfPosts_whenGroupedByTypeAndAveragingLikes_thenGetAMapBetweenTypeAndAverageNumberOfLikes() {
+        Map<BlogPostType, Double> averageLikesPerType = posts.stream()
+            .collect(groupingBy(BlogPost::getType, averagingInt(BlogPost::getLikes)));
+
+        assertEquals(25, averageLikesPerType.get(BlogPostType.NEWS)
+            .intValue());
+        assertEquals(20, averageLikesPerType.get(BlogPostType.GUIDE)
+            .intValue());
+        assertEquals(10, averageLikesPerType.get(BlogPostType.REVIEW)
+            .intValue());
+    }
+
+    @Test
+    public void givenAListOfPosts_whenGroupedByTypeAndCounted_thenGetAMapBetweenTypeAndNumberOfPosts() {
+        Map<BlogPostType, Long> numberOfPostsPerType = posts.stream()
+            .collect(groupingBy(BlogPost::getType, counting()));
+
+        assertEquals(2, numberOfPostsPerType.get(BlogPostType.NEWS)
+            .intValue());
+        assertEquals(1, numberOfPostsPerType.get(BlogPostType.GUIDE)
+            .intValue());
+        assertEquals(2, numberOfPostsPerType.get(BlogPostType.REVIEW)
+            .intValue());
+    }
+
+    @Test
+    public void givenAListOfPosts_whenGroupedByTypeAndMaxingLikes_thenGetAMapBetweenTypeAndMaximumNumberOfLikes() {
+        Map<BlogPostType, Optional<BlogPost>> maxLikesPerPostType = posts.stream()
+            .collect(groupingBy(BlogPost::getType, maxBy(comparingInt(BlogPost::getLikes))));
+
+        assertTrue(maxLikesPerPostType.get(BlogPostType.NEWS)
+            .isPresent());
+        assertEquals(35, maxLikesPerPostType.get(BlogPostType.NEWS)
+            .get()
+            .getLikes());
+
+        assertTrue(maxLikesPerPostType.get(BlogPostType.GUIDE)
+            .isPresent());
+        assertEquals(20, maxLikesPerPostType.get(BlogPostType.GUIDE)
+            .get()
+            .getLikes());
+
+        assertTrue(maxLikesPerPostType.get(BlogPostType.REVIEW)
+            .isPresent());
+        assertEquals(15, maxLikesPerPostType.get(BlogPostType.REVIEW)
+            .get()
+            .getLikes());
+    }
+
+    @Test
+    public void givenAListOfPosts_whenGroupedByAuthorAndThenByType_thenGetAMapBetweenAuthorAndMapsBetweenTypeAndBlogPosts() {
+        Map<String, Map<BlogPostType, List<BlogPost>>> map = posts.stream()
+            .collect(groupingBy(BlogPost::getAuthor, groupingBy(BlogPost::getType)));
+
+        assertEquals(1, map.get("Author 1")
+            .get(BlogPostType.NEWS)
+            .size());
+        assertEquals(1, map.get("Author 1")
+            .get(BlogPostType.GUIDE)
+            .size());
+        assertEquals(1, map.get("Author 1")
+            .get(BlogPostType.REVIEW)
+            .size());
+
+        assertEquals(1, map.get("Author 2")
+            .get(BlogPostType.NEWS)
+            .size());
+        assertEquals(1, map.get("Author 2")
+            .get(BlogPostType.REVIEW)
+            .size());
+        assertNull(map.get("Author 2")
+            .get(BlogPostType.GUIDE));
+    }
+
+    @Test
+    public void givenAListOfPosts_whenGroupedByTypeAndSummarizingLikes_thenGetAMapBetweenTypeAndSummary() {
+        Map<BlogPostType, IntSummaryStatistics> likeStatisticsPerType = posts.stream()
+            .collect(groupingBy(BlogPost::getType, summarizingInt(BlogPost::getLikes)));
+
+        IntSummaryStatistics newsLikeStatistics = likeStatisticsPerType.get(BlogPostType.NEWS);
+
+        assertEquals(2, newsLikeStatistics.getCount());
+        assertEquals(50, newsLikeStatistics.getSum());
+        assertEquals(25.0, newsLikeStatistics.getAverage(), 0.001);
+        assertEquals(35, newsLikeStatistics.getMax());
+        assertEquals(15, newsLikeStatistics.getMin());
+    }
+
+    @Test
+    public void givenAListOfPosts_whenGroupedByComplexMapKeyType_thenGetAMapBetweenTupleAndList() {
+        Map<Tuple, List<BlogPost>> postsPerTypeAndAuthor = posts.stream()
+            .collect(groupingBy(post -> new Tuple(post.getType(), post.getAuthor())));
+
+        List<BlogPost> result = postsPerTypeAndAuthor.get(new Tuple(BlogPostType.GUIDE, "Author 1"));
+
+        assertThat(result.size()).isEqualTo(1);
+
+        BlogPost blogPost = result.get(0);
+
+        assertThat(blogPost.getTitle()).isEqualTo("Programming guide");
+        assertThat(blogPost.getType()).isEqualTo(BlogPostType.GUIDE);
+        assertThat(blogPost.getAuthor()).isEqualTo("Author 1");
+    }
+}

core-java-modules/core-java-8/src/test/java/com/ossez/nullsafecollectionstreams/NullSafeCollectionStreamsUsingCommonsEmptyIfNullUnitTest.java

@@ -0,0 +1,41 @@
+package com.ossez.nullsafecollectionstreams;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.stream.Stream;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+
+public class NullSafeCollectionStreamsUsingCommonsEmptyIfNullUnitTest {
+
+    private final NullSafeCollectionStreamsUsingCommonsEmptyIfNull instance = 
+            new NullSafeCollectionStreamsUsingCommonsEmptyIfNull();
+
+    @Test
+    public void whenCollectionIsNull_thenExpectAnEmptyStream() {
+        Collection<String> collection = null;
+        Stream<String> expResult = Stream.empty();
+        Stream<String> result = instance.collectionAsStream(collection);
+        assertStreamEquals(expResult, result);
+
+    }
+
+    @Test
+    public void whenCollectionHasElements_thenExpectAStreamOfExactlyTheSameElements() {
+
+        Collection<String> collection = Arrays.asList("a", "b", "c");
+        Stream<String> expResult = Arrays.stream(new String[] { "a", "b", "c" });
+        Stream<String> result = instance.collectionAsStream(collection);
+        assertStreamEquals(expResult, result);
+    }
+
+    private static void assertStreamEquals(Stream<?> s1, Stream<?> s2) {
+        Iterator<?> iter1 = s1.iterator(), iter2 = s2.iterator();
+        while (iter1.hasNext() && iter2.hasNext())
+            assertEquals(iter1.next(), iter2.next());
+        assert !iter1.hasNext() && !iter2.hasNext();
+    }
+    
+}

core-java-modules/core-java-8/src/test/java/com/ossez/nullsafecollectionstreams/NullSafeCollectionStreamsUsingJava8OptionalContainerUnitTest.java

@@ -0,0 +1,50 @@
+/*
+ * To change this license header, choose License Headers in Project Properties.
+ * To change this template file, choose Tools | Templates
+ * and open the template in the editor.
+ */
+package com.ossez.nullsafecollectionstreams;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.stream.Stream;
+
+import org.junit.Test;
+
+/**
+ *
+ * @author Kwaje Anthony <kwajeanthony@gmail.com>
+ */
+public class NullSafeCollectionStreamsUsingJava8OptionalContainerUnitTest {
+
+    private final NullSafeCollectionStreamsUsingJava8OptionalContainer instance = new NullSafeCollectionStreamsUsingJava8OptionalContainer();
+
+    @Test
+    public void whenCollectionIsNull_thenExpectAnEmptyStream() {
+        Collection<String> collection = null;
+        Stream<String> expResult = Stream.empty();
+        Stream<String> result = instance.collectionAsStream(collection);
+        assertStreamEquals(expResult, result);
+
+    }
+
+    @Test
+    public void whenCollectionHasElements_thenExpectAStreamOfExactlyTheSameElements() {
+
+        Collection<String> collection = Arrays.asList("a", "b", "c");
+        Stream<String> expResult = Arrays.stream(new String[] { "a", "b", "c" });
+        Stream<String> result = instance.collectionAsStream(collection);
+        assertStreamEquals(expResult, result);
+    }
+
+    private static void assertStreamEquals(Stream<?> s1, Stream<?> s2) {
+        Iterator<?> iter1 = s1.iterator(), iter2 = s2.iterator();
+        while (iter1.hasNext() && iter2.hasNext())
+            assertEquals(iter1.next(), iter2.next());
+        assert !iter1.hasNext() && !iter2.hasNext();
+    }
+
+}

core-java-modules/core-java-8/src/test/java/com/ossez/nullsafecollectionstreams/NullSafeCollectionStreamsUsingNullDereferenceCheckUnitTest.java

@@ -0,0 +1,45 @@
+
+package com.ossez.nullsafecollectionstreams;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.stream.Stream;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+/**
+ *
+ * @author Kwaje Anthony <kwajeanthony@gmail.com>
+ */
+public class NullSafeCollectionStreamsUsingNullDereferenceCheckUnitTest {
+
+    private final NullSafeCollectionStreamsUsingNullDereferenceCheck instance = 
+            new NullSafeCollectionStreamsUsingNullDereferenceCheck();
+
+    @Test
+    public void whenCollectionIsNull_thenExpectAnEmptyStream() {
+        Collection<String> collection = null;
+        Stream<String> expResult = Stream.empty();
+        Stream<String> result = instance.collectionAsStream(collection);
+        assertStreamEquals(expResult, result);
+
+    }
+
+    @Test
+    public void whenCollectionHasElements_thenExpectAStreamOfExactlyTheSameElements() {
+
+        Collection<String> collection = Arrays.asList("a", "b", "c");
+        Stream<String> expResult = Arrays.stream(new String[] { "a", "b", "c" });
+        Stream<String> result = instance.collectionAsStream(collection);
+        assertStreamEquals(expResult, result);
+    }
+
+    private static void assertStreamEquals(Stream<?> s1, Stream<?> s2) {
+        Iterator<?> iter1 = s1.iterator(), iter2 = s2.iterator();
+        while (iter1.hasNext() && iter2.hasNext())
+            assertEquals(iter1.next(), iter2.next());
+        assert !iter1.hasNext() && !iter2.hasNext();
+    }
+
+}

core-java-modules/core-java-8/src/test/java/com/ossez/spliteratorAPI/ExecutorUnitTest.java

@@ -0,0 +1,44 @@
+package com.ossez.spliteratorAPI;
+
+import java.util.Arrays;
+import java.util.Spliterator;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+import static org.assertj.core.api.Assertions.*;
+import org.junit.Before;
+import org.junit.Test;
+
+public class ExecutorUnitTest {
+	Article article;
+	Stream<Author> stream;
+	Spliterator<Author> spliterator;
+	Spliterator<Article> split1;
+	Spliterator<Article> split2;
+
+	@Before
+	public void init() {
+		article = new Article(Arrays.asList(new Author("Ahmad", 0), new Author("Eugen", 0), new Author("Alice", 1),
+				new Author("Alice", 1), new Author("Mike", 0), new Author("Alice", 1), new Author("Mike", 0),
+				new Author("Alice", 1), new Author("Mike", 0), new Author("Alice", 1), new Author("Mike", 0),
+				new Author("Mike", 0), new Author("Alice", 1), new Author("Mike", 0), new Author("Alice", 1),
+				new Author("Mike", 0), new Author("Alice", 1), new Author("Mike", 0), new Author("Alice", 1),
+				new Author("Mike", 0), new Author("Michał", 0), new Author("Loredana", 1)), 0);
+		stream = article.getListOfAuthors().stream();
+		split1 = Executor.generateElements().spliterator();
+		split2 = split1.trySplit();
+		spliterator = new RelatedAuthorSpliterator(article.getListOfAuthors());
+	}
+
+	@Test
+	public void givenAstreamOfAuthors_whenProcessedInParallelWithCustomSpliterator_coubtProducessRightOutput() {
+		Stream<Author> stream2 = StreamSupport.stream(spliterator, true);
+		assertThat(Executor.countAutors(stream2.parallel())).isEqualTo(9);
+	}
+
+	@Test
+	public void givenSpliterator_whenAppliedToAListOfArticle_thenSplittedInHalf() {
+		assertThat(new Task(split1).call()).containsSequence(Executor.generateElements().size() / 2 + "");
+		assertThat(new Task(split2).call()).containsSequence(Executor.generateElements().size() / 2 + "");
+	}
+}

core-java-modules/core-java-8/src/test/java/com/ossez/strategy/StrategyDesignPatternUnitTest.java

@@ -0,0 +1,72 @@
+package com.ossez.strategy;
+
+import org.junit.Test;
+
+import java.math.BigDecimal;
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.Function;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class StrategyDesignPatternUnitTest {
+    @Test
+    public void shouldDivideByTwo_WhenApplyingStaffDiscounter() {
+        Discounter staffDiscounter = new EasterDiscounter();
+
+        final BigDecimal discountedValue = staffDiscounter
+          .apply(BigDecimal.valueOf(100));
+
+        assertThat(discountedValue)
+          .isEqualByComparingTo(BigDecimal.valueOf(50));
+    }
+
+    @Test
+    public void shouldDivideByTwo_WhenApplyingStaffDiscounterWithAnonyousTypes() {
+        Discounter staffDiscounter = new Discounter() {
+            @Override
+            public BigDecimal apply(BigDecimal amount) {
+                return amount.multiply(BigDecimal.valueOf(0.5));
+            }
+        };
+
+        final BigDecimal discountedValue = staffDiscounter
+          .apply(BigDecimal.valueOf(100));
+
+        assertThat(discountedValue)
+          .isEqualByComparingTo(BigDecimal.valueOf(50));
+    }
+
+    @Test
+    public void shouldDivideByTwo_WhenApplyingStaffDiscounterWithLamda() {
+        Discounter staffDiscounter = amount -> amount.multiply(BigDecimal.valueOf(0.5));
+
+        final BigDecimal discountedValue = staffDiscounter
+          .apply(BigDecimal.valueOf(100));
+
+        assertThat(discountedValue)
+          .isEqualByComparingTo(BigDecimal.valueOf(50));
+    }
+
+    @Test
+    public void shouldApplyAllDiscounts() {
+        List<Discounter> discounters = Arrays.asList(Discounter.christmas(), Discounter.newYear(), Discounter.easter());
+
+        BigDecimal amount = BigDecimal.valueOf(100);
+
+        final Discounter combinedDiscounter = discounters
+          .stream()
+          .reduce(v -> v, Discounter::combine);
+
+        combinedDiscounter.apply(amount);
+    }
+
+    @Test
+    public void shouldChainDiscounters() {
+        final Function<BigDecimal, BigDecimal> combinedDiscounters = Discounter
+          .christmas()
+          .andThen(Discounter.newYear());
+
+        combinedDiscounters.apply(BigDecimal.valueOf(100));
+    }
+}

core-java-modules/core-java-8/src/test/java/com/ossez/streamreduce/tests/StreamReduceManualTest.java

@@ -0,0 +1,153 @@
+package com.ossez.streamreduce.tests;
+
+import com.ossez.streamreduce.entities.Rating;
+import com.ossez.streamreduce.entities.Review;
+import com.ossez.streamreduce.entities.User;
+import com.ossez.streamreduce.utilities.NumberUtils;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class StreamReduceManualTest {
+
+    @Test
+    public void givenIntegerList_whenReduceWithSumAccumulatorLambda_thenCorrect() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        
+        int result = numbers.stream().reduce(0, (a, b) -> a + b);
+        
+        assertThat(result).isEqualTo(21);
+    }
+
+    @Test
+    public void givenIntegerList_whenReduceWithSumAccumulatorMethodReference_thenCorrect() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        
+        int result = numbers.stream().reduce(0, Integer::sum);
+        
+        assertThat(result).isEqualTo(21);
+    }
+
+    @Test
+    public void givenStringList_whenReduceWithConcatenatorAccumulatorLambda_thenCorrect() {
+        List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
+        
+        String result = letters.stream().reduce("", (a, b) -> a + b);
+        
+        assertThat(result).isEqualTo("abcde");
+    }
+
+    @Test
+    public void givenStringList_whenReduceWithConcatenatorAccumulatorMethodReference_thenCorrect() {
+        List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
+        
+        String result = letters.stream().reduce("", String::concat);
+        
+        assertThat(result).isEqualTo("abcde");
+    }
+
+    @Test
+    public void givenStringList_whenReduceWithUppercaseConcatenatorAccumulator_thenCorrect() {
+        List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
+        
+        String result = letters.stream().reduce("", (a, b) -> a.toUpperCase() + b.toUpperCase());
+        
+        assertThat(result).isEqualTo("ABCDE");
+    }
+
+    @Test
+    public void givenUserList_whenReduceWithAgeAccumulatorAndSumCombiner_thenCorrect() {
+        List<User> users = Arrays.asList(new User("John", 30), new User("Julie", 35));
+        
+        int result = users.stream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
+        
+        assertThat(result).isEqualTo(65);
+    }
+
+    @Test
+    public void givenUserList_whenReduceWithGreaterAgeAccumulator_thenFindsOldest() {
+        List<User> users = Arrays.asList(new User("John", 30), new User("Alex", 40), new User("Julie", 35));
+
+        User oldest = users.stream().reduce(users.get(0), (user1, user2) -> user1.getAge() >= user2.getAge() ? user1 : user2);
+
+        assertThat(oldest).isEqualTo(users.get(1));
+    }
+
+    @Test
+    public void givenUserListWithRatings_whenReduceWithGreaterAgeAccumulator_thenFindsOldest() {
+        User john = new User("John", 30);
+        john.getRating().add(new Review(5, ""));
+        john.getRating().add(new Review(3, "not bad"));
+        User julie = new User("Julie", 35);
+        john.getRating().add(new Review(4, "great!"));
+        john.getRating().add(new Review(2, "terrible experience"));
+        john.getRating().add(new Review(4, ""));
+        List<User> users = Arrays.asList(john, julie);
+
+        Rating averageRating = users.stream().reduce(new Rating(), (rating, user) -> Rating.average(rating, user.getRating()), Rating::average);
+
+        assertThat(averageRating.getPoints()).isEqualTo(3.6);
+    }
+
+    @Test
+    public void givenStringList_whenReduceWithParallelStream_thenCorrect() {
+        List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
+        
+        String result = letters.parallelStream().reduce("", String::concat);
+        
+        assertThat(result).isEqualTo("abcde");
+    }
+
+    @Test
+    public void givenNumberUtilsClass_whenCalledDivideListElements_thenCorrect() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        
+        assertThat(NumberUtils.divideListElements(numbers, 1)).isEqualTo(21);
+    }
+
+    @Test
+    public void givenNumberUtilsClass_whenCalledDivideListElementsWithExtractedTryCatchBlock_thenCorrect() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        
+        assertThat(NumberUtils.divideListElementsWithExtractedTryCatchBlock(numbers, 1)).isEqualTo(21);
+    }
+
+    @Test
+    public void givenNumberUtilsClass_whenCalledDivideListElementsWithExtractedTryCatchBlockAndListContainsZero_thenCorrect() {
+        List<Integer> numbers = Arrays.asList(0, 1, 2, 3, 4, 5, 6);
+        
+        assertThat(NumberUtils.divideListElementsWithExtractedTryCatchBlock(numbers, 1)).isEqualTo(21);
+    }
+    
+    @Test
+    public void givenNumberUtilsClass_whenCalledDivideListElementsWithExtractedTryCatchBlockAndDividerIsZero_thenCorrect() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        
+        assertThat(NumberUtils.divideListElementsWithExtractedTryCatchBlock(numbers, 0)).isEqualTo(0);
+    }
+    
+    @Test
+    public void givenStream_whneCalleddivideListElementsWithApplyFunctionMethod_thenCorrect() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        
+        assertThat(NumberUtils.divideListElementsWithApplyFunctionMethod(numbers, 1)).isEqualTo(21);
+    }
+    
+    @Test
+    public void givenTwoStreams_whenCalledReduceOnParallelizedStream_thenFasterExecutionTime() {
+        List<User> userList = new ArrayList<>();
+        for (int i = 0; i <= 1000000; i++) {
+            userList.add(new User("John" + i, i));
+        }
+        long currentTime1 = System.currentTimeMillis();
+        userList.stream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
+        long sequentialExecutionTime = System.currentTimeMillis() -currentTime1;
+        long currentTime2 = System.currentTimeMillis();
+        userList.parallelStream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
+        long parallelizedExecutionTime = System.currentTimeMillis() - currentTime2;
+        
+        assertThat(parallelizedExecutionTime).isLessThan(sequentialExecutionTime);
+    }
+}

core-java-modules/core-java-8/src/test/java/com/ossez/typeinference/TypeInferenceUnitTest.java

@@ -0,0 +1,87 @@
+package com.ossez.typeinference;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.Test;
+
+public class TypeInferenceUnitTest {
+
+    @Test
+    public void givenNoTypeInference_whenInvokingGenericMethodsWithTypeParameters_ObjectsAreCreated() {
+        // Without type inference. code is verbose.
+        Map<String, Map<String, String>> mapOfMaps = new HashMap<String, Map<String, String>>();
+        List<String> strList = Collections.<String> emptyList();
+        List<Integer> intList = Collections.<Integer> emptyList();
+
+        assertTrue(mapOfMaps.isEmpty());
+        assertTrue(strList.isEmpty());
+        assertTrue(intList.isEmpty());
+    }
+
+    @Test
+    public void givenTypeInference_whenInvokingGenericMethodsWithoutTypeParameters_ObjectsAreCreated() {
+        // With type inference. code is concise.
+        List<String> strListInferred = Collections.emptyList();
+        List<Integer> intListInferred = Collections.emptyList();
+
+        assertTrue(strListInferred.isEmpty());
+        assertTrue(intListInferred.isEmpty());
+    }
+
+    @Test
+    public void givenJava7_whenInvokingCostructorWithoutTypeParameters_ObjectsAreCreated() {
+        // Type Inference for constructor using diamond operator.
+        Map<String, Map<String, String>> mapOfMapsInferred = new HashMap<>();
+
+        assertTrue(mapOfMapsInferred.isEmpty());
+        assertEquals("public class java.util.HashMap<K,V>", mapOfMapsInferred.getClass()
+            .toGenericString());
+    }
+
+    static <T> List<T> add(List<T> list, T a, T b) {
+        list.add(a);
+        list.add(b);
+        return list;
+    }
+
+    @Test
+    public void givenGenericMethod_WhenInvokedWithoutExplicitTypes_TypesAreInferred() {
+        // Generalized target-type inference
+        List<String> strListGeneralized = add(new ArrayList<>(), "abc", "def");
+        List<Integer> intListGeneralized = add(new ArrayList<>(), 1, 2);
+        List<Number> numListGeneralized = add(new ArrayList<>(), 1, 2.0);
+
+        assertEquals("public class java.util.ArrayList<E>", strListGeneralized.getClass()
+            .toGenericString());
+        assertFalse(intListGeneralized.isEmpty());
+        assertEquals(2, numListGeneralized.size());
+    }
+
+    @Test
+    public void givenLambdaExpressions_whenParameterTypesNotSpecified_ParameterTypesAreInferred() {
+        // Type Inference and Lambda Expressions.
+        List<Integer> intList = Arrays.asList(5, 3, 4, 2, 1);
+        Collections.sort(intList, (a, b) -> {
+            assertEquals("java.lang.Integer", a.getClass().getName());
+            return a.compareTo(b);
+        });
+        assertEquals("[1, 2, 3, 4, 5]", Arrays.toString(intList.toArray()));
+
+        List<String> strList = Arrays.asList("Red", "Blue", "Green");
+        Collections.sort(strList, (a, b) -> {
+            assertEquals("java.lang.String", a.getClass().getName());
+            return a.compareTo(b);
+        });
+        assertEquals("[Blue, Green, Red]", Arrays.toString(strList.toArray()));
+    }
+
+}

core-java-modules/core-java-8/src/test/java/com/ossez/util/CurrentDateTimeUnitTest.java

@@ -0,0 +1,42 @@
+package com.ossez.util;
+
+import static org.junit.Assert.assertEquals;
+
+import java.time.Clock;
+import java.time.Instant;
+import java.time.LocalDate;
+import java.time.LocalTime;
+import java.time.ZoneId;
+import java.time.temporal.ChronoField;
+
+import org.junit.Test;
+
+public class CurrentDateTimeUnitTest {
+
+    private static final Clock clock = Clock.fixed(Instant.parse("2016-10-09T15:10:30.00Z"), ZoneId.of("UTC"));
+
+    @Test
+    public void shouldReturnCurrentDate() {
+        final LocalDate now = LocalDate.now(clock);
+
+        assertEquals(9, now.get(ChronoField.DAY_OF_MONTH));
+        assertEquals(10, now.get(ChronoField.MONTH_OF_YEAR));
+        assertEquals(2016, now.get(ChronoField.YEAR));
+    }
+
+    @Test
+    public void shouldReturnCurrentTime() {
+        final LocalTime now = LocalTime.now(clock);
+
+        assertEquals(15, now.get(ChronoField.HOUR_OF_DAY));
+        assertEquals(10, now.get(ChronoField.MINUTE_OF_HOUR));
+        assertEquals(30, now.get(ChronoField.SECOND_OF_MINUTE));
+    }
+
+    @Test
+    public void shouldReturnCurrentTimestamp() {
+        final Instant now = Instant.now(clock);
+
+        assertEquals(clock.instant().getEpochSecond(), now.getEpochSecond());
+    }
+}

core-java-modules/core-java-8/src/test/resources/.gitignore

@@ -0,0 +1,13 @@
+*.class
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+
+# Packaged files #
+*.jar
+*.war
+*.ear