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Java 8 grouping by collector pull request (#1102) 

* Char array to string and string to char array test cases added

* Minor code renames

* Added groupingBy collector unit tests

* Added test case for int summary calculation on grouped results

* Added the grouping by classes to the main source path

* Reverting char array to string test class

* Reverting char array to string test class

* Reverting char array to string test class

* Reverting char array to string test class
This commit is contained in:
Tryfon 2017-02-07 12:36:06 +02:00 committed by Sunil Mogadati
parent 178f49e485
commit c13453d772
3 changed files with 173 additions and 0 deletions
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36
core-java/src/main/java/com/baeldung/java_8_features/groupingby/BlogPost.java Normal file
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package com.baeldung.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 + '}';
}
}

5
core-java/src/main/java/com/baeldung/java_8_features/groupingby/BlogPostType.java Normal file
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package com.baeldung.java_8_features.groupingby;
public enum BlogPostType {
NEWS, REVIEW, GUIDE
}

132
core-java/src/test/java/com/baeldung/java8/Java8GroupingByCollectorUnitTest.java Normal file
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package com.baeldung.java8;
import org.junit.Test;
import com.baeldung.java_8_features.groupingby.BlogPost;
import com.baeldung.java_8_features.groupingby.BlogPostType;
import java.util.*;
import java.util.concurrent.ConcurrentMap;
import static java.util.Comparator.comparingInt;
import static java.util.stream.Collectors.*;
import static org.junit.Assert.*;
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());
}
}