这是indexloc提供的服务，不要输入任何密码
Skip to content

BAEL-8484: Merge articles on Java Collectors #17525

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Sep 27, 2024
Merged

BAEL-8484: Merge articles on Java Collectors #17525

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
61 changes: 0 additions & 61 deletions ...ements/src/test/java/com/baeldung/java9/language/stream/CollectorImprovementUnitTest.java
View file
Open in desktop

This file was deleted.

22 changes: 22 additions & 0 deletions ...-modules/core-java-streams-simple/src/main/java/com/baeldung/streams/collectors/Blog.java
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,22 @@
package com.baeldung.streams.collectors;

import java.util.List;

public class Blog {

private String authorName;
private List<String> comments;

public Blog(String authorName, String... comments) {
this.authorName = authorName;
this.comments = List.of(comments);
}

public String getAuthorName() {
return this.authorName;
}

public List<String> getComments() {
return this.comments;
}
}
57 changes: 57 additions & 0 deletions ...ms-simple/src/test/java/com/baeldung/streams/collectors/CollectorImprovementUnitTest.java
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,57 @@
package com.baeldung.streams.collectors;

import static org.junit.Assert.assertEquals;

import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

import org.junit.jupiter.api.Test;

class CollectorImprovementUnitTest {

@Test
void givenList_whenSatifyPredicate_thenMapValueWithOccurences() {
List<Integer> numbers = List.of(1, 2, 3, 5, 5);

Map<Integer, Long> result = numbers.stream()
.filter(val -> val > 3)
.collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

assertEquals(1, result.size());

result = numbers.stream()
.collect(Collectors.groupingBy(Function.identity(), Collectors.filtering(val -> val > 3, Collectors.counting())));

assertEquals(4, result.size());
}

@Test
void givenListOfBlogs_whenAuthorName_thenMapAuthorWithComments() {
Blog blog1 = new Blog("1", "Nice", "Very Nice");
Blog blog2 = new Blog("2", "Disappointing", "Ok", "Could be better");
List<Blog> blogs = List.of(blog1, blog2);

Map<String, List<List<String>>> authorComments1 = blogs.stream()
.collect(Collectors.groupingBy(Blog::getAuthorName, Collectors.mapping(Blog::getComments, Collectors.toList())));

assertEquals(2, authorComments1.size());
assertEquals(2, authorComments1.get("1")
.get(0)
.size());
assertEquals(3, authorComments1.get("2")
.get(0)
.size());

Map<String, List<String>> authorComments2 = blogs.stream()
.collect(Collectors.groupingBy(Blog::getAuthorName, Collectors.flatMapping(blog -> blog.getComments()
.stream(), Collectors.toList())));

assertEquals(2, authorComments2.size());
assertEquals(2, authorComments2.get("1")
.size());
assertEquals(3, authorComments2.get("2")
.size());
}
}