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[JAVA-12051] Moved code to core-java-streams-simple for ebook (#14889)

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This commit is contained in:
panos-kakos
2023-10-13 14:41:35 +03:00
committed by GitHub
parent ff826f0d08
commit ee98df03f4
38 changed files with 200 additions and 76 deletions
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core-java-modules/core-java-16/README.md
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- [Guide to mapMulti in Stream API](https://www.baeldung.com/java-mapmulti)
- [Collecting Stream Elements into a List in Java](https://www.baeldung.com/java-stream-to-list-collecting)
- [New Features in Java 16](https://www.baeldung.com/java-16-new-features)
- [Guide to Java 8 groupingBy Collector](https://www.baeldung.com/java-groupingby-collector)
- [Value-Based Classes in Java](https://www.baeldung.com/java-value-based-classes)
core-java-modules/core-java-16/src/main/java/com/baeldung/java_16_features/groupingby/BlogPost.java
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package com.baeldung.java_16_features.groupingby;
import java.util.IntSummaryStatistics;
public class BlogPost {
private String title;
private String author;
private BlogPostType type;
private int likes;
record AuthPostTypesLikes(String author, BlogPostType type, int likes) {};
record PostCountTitlesLikesStats(long postCount, String titles, IntSummaryStatistics likesStats){};
record TitlesBoundedSumOfLikes(String titles, int boundedSumOfLikes) {};
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-16/src/main/java/com/baeldung/java_16_features/groupingby/BlogPostType.java
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package com.baeldung.java_16_features.groupingby;
public enum BlogPostType {
NEWS, REVIEW, GUIDE
}
core-java-modules/core-java-16/src/main/java/com/baeldung/java_16_features/groupingby/Tuple.java
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@@ -1,41 +0,0 @@
package com.baeldung.java_16_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-16/src/test/java/com/baeldung/java_16_features/groupingby/JavaGroupingByCollectorUnitTest.java
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@@ -1,302 +0,0 @@
package com.baeldung.java_16_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.collectingAndThen;
import static java.util.stream.Collectors.toMap;
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.assertj.core.api.Assertions.offset;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNull;
import static org.junit.jupiter.api.Assertions.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.apache.commons.lang3.tuple.ImmutablePair;
import org.apache.commons.lang3.tuple.Pair;
import org.junit.jupiter.api.Test;
public class JavaGroupingByCollectorUnitTest {
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_whenGroupedByComplexMapPairKeyType_thenGetAMapBetweenPairAndList() {
Map<Pair<BlogPostType, String>, List<BlogPost>> postsPerTypeAndAuthor = posts.stream()
.collect(groupingBy(post -> new ImmutablePair<>(post.getType(), post.getAuthor())));
List<BlogPost> result = postsPerTypeAndAuthor.get(new ImmutablePair<>(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");
}
@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");
}
@Test
public void givenAListOfPosts_whenGroupedByRecord_thenGetAMapBetweenRecordAndList() {
Map<BlogPost.AuthPostTypesLikes, List<BlogPost>> postsPerTypeAndAuthor = posts.stream()
.collect(groupingBy(post -> new BlogPost.AuthPostTypesLikes(post.getAuthor(), post.getType(), post.getLikes())));
List<BlogPost> result = postsPerTypeAndAuthor.get(new BlogPost.AuthPostTypesLikes("Author 1", BlogPostType.GUIDE, 20));
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");
assertThat(blogPost.getLikes()).isEqualTo(20);
}
@Test
public void givenListOfPosts_whenGroupedByAuthor_thenGetAMapUsingCollectingAndThen() {
Map<String, BlogPost.PostCountTitlesLikesStats> postsPerAuthor = posts.stream()
.collect(groupingBy(BlogPost::getAuthor, collectingAndThen(toList(), list -> {
long count = list.stream()
.map(BlogPost::getTitle)
.collect(counting());
String titles = list.stream()
.map(BlogPost::getTitle)
.collect(joining(" : "));
IntSummaryStatistics summary = list.stream()
.collect(summarizingInt(BlogPost::getLikes));
return new BlogPost.PostCountTitlesLikesStats(count, titles, summary);
})));
BlogPost.PostCountTitlesLikesStats result = postsPerAuthor.get("Author 1");
assertThat(result.postCount()).isEqualTo(3L);
assertThat(result.titles()).isEqualTo("News item 1 : Programming guide : Tech review 2");
assertThat(result.likesStats().getMax()).isEqualTo(20);
assertThat(result.likesStats().getMin()).isEqualTo(15);
assertThat(result.likesStats().getAverage()).isEqualTo(16.666d, offset(0.001d));
}
@Test
public void givenListOfPosts_whenGroupedByAuthor_thenGetAMapUsingToMap() {
int maxValLikes = 17;
Map<String, BlogPost.TitlesBoundedSumOfLikes> postsPerAuthor = posts.stream()
.collect(toMap(BlogPost::getAuthor, post -> {
int likes = (post.getLikes() > maxValLikes) ? maxValLikes : post.getLikes();
return new BlogPost.TitlesBoundedSumOfLikes(post.getTitle(), likes);
}, (u1, u2) -> {
int likes = (u2.boundedSumOfLikes() > maxValLikes) ? maxValLikes : u2.boundedSumOfLikes();
return new BlogPost.TitlesBoundedSumOfLikes(u1.titles()
.toUpperCase() + " : "
+ u2.titles()
.toUpperCase(),
u1.boundedSumOfLikes() + likes);
}));
BlogPost.TitlesBoundedSumOfLikes result = postsPerAuthor.get("Author 1");
assertThat(result.titles()).isEqualTo("NEWS ITEM 1 : PROGRAMMING GUIDE : TECH REVIEW 2");
assertThat(result.boundedSumOfLikes()).isEqualTo(47);
}
}