BAEL-5065-v2 deleted files already moved to core-java-16 module
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Loredana Crusoveanu
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47249aa1ff
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b0834a7c3f
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@ -4,7 +4,6 @@ This module contains articles about Java 8 core features
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### Relevant Articles:
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- [New Features in Java 8](https://www.baeldung.com/java-8-new-features)
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- [Guide to Java 8 groupingBy Collector](https://www.baeldung.com/java-groupingby-collector)
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- [Strategy Design Pattern in Java 8](https://www.baeldung.com/java-strategy-pattern)
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- [Guide to Java 8 Comparator.comparing()](https://www.baeldung.com/java-8-comparator-comparing)
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- [Guide to the Java 8 forEach](https://www.baeldung.com/foreach-java)
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@ -1,36 +0,0 @@
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package com.baeldung.java_8_features.groupingby;
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public class BlogPost {
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private String title;
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private String author;
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private BlogPostType type;
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private int likes;
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public BlogPost(String title, String author, BlogPostType type, int likes) {
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this.title = title;
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this.author = author;
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this.type = type;
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this.likes = likes;
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}
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public String getTitle() {
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return title;
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}
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public String getAuthor() {
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return author;
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}
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public BlogPostType getType() {
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return type;
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}
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public int getLikes() {
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return likes;
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}
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@Override
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public String toString() {
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return "BlogPost{" + "title='" + title + '\'' + ", type=" + type + ", likes=" + likes + '}';
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}
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}
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@ -1,5 +0,0 @@
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package com.baeldung.java_8_features.groupingby;
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public enum BlogPostType {
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NEWS, REVIEW, GUIDE
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}
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@ -1,41 +0,0 @@
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package com.baeldung.java_8_features.groupingby;
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import java.util.Objects;
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public class Tuple {
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private final BlogPostType type;
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private final String author;
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public Tuple(BlogPostType type, String author) {
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this.type = type;
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this.author = author;
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}
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public BlogPostType getType() {
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return type;
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}
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public String getAuthor() {
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return author;
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}
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@Override
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public boolean equals(Object o) {
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if (this == o)
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return true;
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if (o == null || getClass() != o.getClass())
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return false;
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Tuple tuple = (Tuple) o;
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return type == tuple.type && author.equals(tuple.author);
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}
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@Override
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public int hashCode() {
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return Objects.hash(type, author);
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}
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@Override
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public String toString() {
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return "Tuple{" + "type=" + type + ", author='" + author + '\'' + '}';
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}
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}
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@ -1,215 +0,0 @@
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package com.baeldung.java_8_features.groupingby;
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import static java.util.Comparator.comparingInt;
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import static java.util.stream.Collectors.averagingInt;
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import static java.util.stream.Collectors.counting;
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import static java.util.stream.Collectors.groupingBy;
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import static java.util.stream.Collectors.groupingByConcurrent;
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import static java.util.stream.Collectors.joining;
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import static java.util.stream.Collectors.mapping;
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import static java.util.stream.Collectors.maxBy;
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import static java.util.stream.Collectors.summarizingInt;
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import static java.util.stream.Collectors.summingInt;
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import static java.util.stream.Collectors.toList;
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import static java.util.stream.Collectors.toSet;
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import static org.assertj.core.api.Assertions.assertThat;
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import static org.junit.Assert.assertEquals;
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import static org.junit.Assert.assertNull;
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import static org.junit.Assert.assertTrue;
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import java.util.Arrays;
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import java.util.EnumMap;
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import java.util.IntSummaryStatistics;
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import java.util.List;
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import java.util.Map;
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import java.util.Optional;
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import java.util.Set;
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import java.util.concurrent.ConcurrentMap;
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import org.junit.Test;
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public class Java8GroupingByCollectorUnitTest {
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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),
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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));
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@Test
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public void givenAListOfPosts_whenGroupedByType_thenGetAMapBetweenTypeAndPosts() {
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Map<BlogPostType, List<BlogPost>> postsPerType = posts.stream()
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.collect(groupingBy(BlogPost::getType));
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assertEquals(2, postsPerType.get(BlogPostType.NEWS)
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.size());
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assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
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.size());
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assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
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.size());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeAndTheirTitlesAreJoinedInAString_thenGetAMapBetweenTypeAndCsvTitles() {
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Map<BlogPostType, String> postsPerType = posts.stream()
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.collect(groupingBy(BlogPost::getType, mapping(BlogPost::getTitle, joining(", ", "Post titles: [", "]"))));
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assertEquals("Post titles: [News item 1, News item 2]", postsPerType.get(BlogPostType.NEWS));
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assertEquals("Post titles: [Programming guide]", postsPerType.get(BlogPostType.GUIDE));
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assertEquals("Post titles: [Tech review 1, Tech review 2]", postsPerType.get(BlogPostType.REVIEW));
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeAndSumTheLikes_thenGetAMapBetweenTypeAndPostLikes() {
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Map<BlogPostType, Integer> likesPerType = posts.stream()
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.collect(groupingBy(BlogPost::getType, summingInt(BlogPost::getLikes)));
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assertEquals(50, likesPerType.get(BlogPostType.NEWS)
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.intValue());
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assertEquals(20, likesPerType.get(BlogPostType.REVIEW)
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.intValue());
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assertEquals(20, likesPerType.get(BlogPostType.GUIDE)
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.intValue());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeInAnEnumMap_thenGetAnEnumMapBetweenTypeAndPosts() {
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EnumMap<BlogPostType, List<BlogPost>> postsPerType = posts.stream()
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.collect(groupingBy(BlogPost::getType, () -> new EnumMap<>(BlogPostType.class), toList()));
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assertEquals(2, postsPerType.get(BlogPostType.NEWS)
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.size());
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assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
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.size());
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assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
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.size());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeInSets_thenGetAMapBetweenTypesAndSetsOfPosts() {
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Map<BlogPostType, Set<BlogPost>> postsPerType = posts.stream()
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.collect(groupingBy(BlogPost::getType, toSet()));
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assertEquals(2, postsPerType.get(BlogPostType.NEWS)
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.size());
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assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
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.size());
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assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
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.size());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeConcurrently_thenGetAMapBetweenTypeAndPosts() {
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ConcurrentMap<BlogPostType, List<BlogPost>> postsPerType = posts.parallelStream()
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.collect(groupingByConcurrent(BlogPost::getType));
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assertEquals(2, postsPerType.get(BlogPostType.NEWS)
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.size());
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assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
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.size());
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assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
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.size());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeAndAveragingLikes_thenGetAMapBetweenTypeAndAverageNumberOfLikes() {
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Map<BlogPostType, Double> averageLikesPerType = posts.stream()
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.collect(groupingBy(BlogPost::getType, averagingInt(BlogPost::getLikes)));
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assertEquals(25, averageLikesPerType.get(BlogPostType.NEWS)
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.intValue());
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assertEquals(20, averageLikesPerType.get(BlogPostType.GUIDE)
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.intValue());
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assertEquals(10, averageLikesPerType.get(BlogPostType.REVIEW)
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.intValue());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeAndCounted_thenGetAMapBetweenTypeAndNumberOfPosts() {
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Map<BlogPostType, Long> numberOfPostsPerType = posts.stream()
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.collect(groupingBy(BlogPost::getType, counting()));
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assertEquals(2, numberOfPostsPerType.get(BlogPostType.NEWS)
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.intValue());
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assertEquals(1, numberOfPostsPerType.get(BlogPostType.GUIDE)
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.intValue());
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assertEquals(2, numberOfPostsPerType.get(BlogPostType.REVIEW)
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.intValue());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeAndMaxingLikes_thenGetAMapBetweenTypeAndMaximumNumberOfLikes() {
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Map<BlogPostType, Optional<BlogPost>> maxLikesPerPostType = posts.stream()
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.collect(groupingBy(BlogPost::getType, maxBy(comparingInt(BlogPost::getLikes))));
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assertTrue(maxLikesPerPostType.get(BlogPostType.NEWS)
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.isPresent());
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assertEquals(35, maxLikesPerPostType.get(BlogPostType.NEWS)
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.get()
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.getLikes());
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assertTrue(maxLikesPerPostType.get(BlogPostType.GUIDE)
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.isPresent());
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assertEquals(20, maxLikesPerPostType.get(BlogPostType.GUIDE)
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.get()
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.getLikes());
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assertTrue(maxLikesPerPostType.get(BlogPostType.REVIEW)
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.isPresent());
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assertEquals(15, maxLikesPerPostType.get(BlogPostType.REVIEW)
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.get()
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.getLikes());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByAuthorAndThenByType_thenGetAMapBetweenAuthorAndMapsBetweenTypeAndBlogPosts() {
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Map<String, Map<BlogPostType, List<BlogPost>>> map = posts.stream()
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.collect(groupingBy(BlogPost::getAuthor, groupingBy(BlogPost::getType)));
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assertEquals(1, map.get("Author 1")
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.get(BlogPostType.NEWS)
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.size());
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assertEquals(1, map.get("Author 1")
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.get(BlogPostType.GUIDE)
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.size());
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assertEquals(1, map.get("Author 1")
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.get(BlogPostType.REVIEW)
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.size());
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assertEquals(1, map.get("Author 2")
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.get(BlogPostType.NEWS)
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.size());
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assertEquals(1, map.get("Author 2")
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.get(BlogPostType.REVIEW)
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.size());
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assertNull(map.get("Author 2")
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.get(BlogPostType.GUIDE));
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeAndSummarizingLikes_thenGetAMapBetweenTypeAndSummary() {
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Map<BlogPostType, IntSummaryStatistics> likeStatisticsPerType = posts.stream()
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.collect(groupingBy(BlogPost::getType, summarizingInt(BlogPost::getLikes)));
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IntSummaryStatistics newsLikeStatistics = likeStatisticsPerType.get(BlogPostType.NEWS);
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assertEquals(2, newsLikeStatistics.getCount());
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assertEquals(50, newsLikeStatistics.getSum());
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assertEquals(25.0, newsLikeStatistics.getAverage(), 0.001);
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assertEquals(35, newsLikeStatistics.getMax());
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assertEquals(15, newsLikeStatistics.getMin());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByComplexMapKeyType_thenGetAMapBetweenTupleAndList() {
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Map<Tuple, List<BlogPost>> postsPerTypeAndAuthor = posts.stream()
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.collect(groupingBy(post -> new Tuple(post.getType(), post.getAuthor())));
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List<BlogPost> result = postsPerTypeAndAuthor.get(new Tuple(BlogPostType.GUIDE, "Author 1"));
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assertThat(result.size()).isEqualTo(1);
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BlogPost blogPost = result.get(0);
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assertThat(blogPost.getTitle()).isEqualTo("Programming guide");
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assertThat(blogPost.getType()).isEqualTo(BlogPostType.GUIDE);
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assertThat(blogPost.getAuthor()).isEqualTo("Author 1");
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}
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}
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