10 Java One‑Liners Using Lambda and Stream for Common Tasks

The article lists ten independent Java one‑liners that demonstrate how Java 8 features like lambda expressions, streams, try‑with‑resources, and JAXB can be used to implement common business logic without relying on additional code.

1. Multiply each element in a list/array by 2

int[] ia = range(1, 10).map(i -> i * 2).toArray();
List<Integer> result = range(1, 10).map(i -> i * 2).boxed().collect(toList());

2. Compute the sum of numbers in a collection/array

range(1, 1000).sum();
range(1, 1000).reduce(0, Integer::sum);
Stream.iterate(0, i -> i + 1).limit(1000).reduce(0, Integer::sum);
IntStream.iterate(0, i -> i + 1).limit(1000).reduce(0, Integer::sum);

3. Check whether a string contains any keyword from a collection

final List<String> keywords = Arrays.asList("brown", "fox", "dog", "pangram");
final String tweet = "The quick brown fox jumps over a lazy dog. #pangram http://www.rinkworks.com/words/pangrams.shtml";
keywords.stream().anyMatch(tweet::contains);
keywords.stream().reduce(false, (b, keyword) -> b || tweet.contains(keyword), (l, r) -> l || r);

4. Read file content (try‑with‑resources)

try (BufferedReader reader = new BufferedReader(new FileReader("data.txt"))) {
    String fileText = reader.lines().reduce("", String::concat);
}

try (BufferedReader reader = new BufferedReader(new FileReader("data.txt"))) {
    List<String> fileLines = reader.lines().collect(toCollection(LinkedList::new));
}

try (Stream<String> lines = Files.lines(new File("data.txt").toPath(), Charset.defaultCharset())) {
    List<String> fileLines = lines.collect(toCollection(LinkedList::new));
}

5. Print the "Happy Birthday" song with conditional text

range(1, 5).boxed().map(i -> {
    out.print("Happy Birthday ");
    if (i == 3) return "dear NAME"; else return "to You";
}).forEach(out::println);

6. Filter and group numbers in a collection

Map<String, List<Integer>> result = Stream.of(49, 58, 76, 82, 88, 90)
    .collect(groupingBy(forPredicate(i -> i > 60, "passed", "failed")));

7. Retrieve and marshal an XML Web Service using JAXB

FeedType feed = JAXB.unmarshal(new URL("http://search.twitter.com/search.atom?&q=java8"), FeedType.class);
JAXB.marshal(feed, System.out);

8. Obtain the minimum and maximum numbers in a collection

int min = Stream.of(14, 35, -7, 46, 98).reduce(Integer::min).get();
min = Stream.of(14, 35, -7, 46, 98).min(Integer::compare).get();
min = Stream.of(14, 35, -7, 46, 98).mapToInt(Integer::new).min();

int max = Stream.of(14, 35, -7, 46, 98).reduce(Integer::max).get();
max = Stream.of(14, 35, -7, 46, 98).max(Integer::compare).get();
max = Stream.of(14, 35, -7, 46, 98).mapToInt(Integer::new).max();

9. Parallel processing

long result = dataList.parallelStream().mapToInt(line -> processItem(line)).sum();

10. Various queries on collections (LINQ‑style in Java)

List<Album> albums = Arrays.asList(unapologetic, tailgates, red);
// Filter albums with at least one track rating >= 4, sort by name, and print
albums.stream()
    .filter(a -> a.tracks.stream().anyMatch(t -> t.rating >= 4))
    .sorted(comparing(album -> album.name))
    .forEach(album -> System.out.println(album.name));

// Merge all tracks from all albums
List<Track> allTracks = albums.stream()
    .flatMap(album -> album.tracks.stream())
    .collect(toList());

// Group tracks by rating
Map<Integer, List<Track>> tracksByRating = allTracks.stream()
    .collect(groupingBy(Track::getRating));

Source: rowkey.me/blog/2017/09/09/java-oneliners/