Java8 Streams Examples

Java 8 introduced the Stream API, which allows you to perform functional-style operations on collections of data. Here are some examples of using the Stream API:

1. Filtering a list of integers:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
List<Integer> evenNumbers = numbers.stream()
                                      .filter(n -> n % 2 == 0)
                                      .collect(Collectors.toList());

2. Mapping a list of strings to a list of their lengths:

List<String> words = Arrays.asList("foo", "bar", "baz", "qux");
List<Integer> wordLengths = words.stream()
                                  .map(String::length)
                                  .collect(Collectors.toList());

3. Summing a list of numbers:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
int sum = numbers.stream()
                 .reduce(0, Integer::sum);

4. Finding the maximum value in a list of numbers:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
Optional<Integer> max = numbers.stream()
                               .max(Integer::compareTo);

5. Counting the number of elements in a list that match a certain condition:

List<String> words = Arrays.asList("foo", "bar", "baz", "qux");
long count = words.stream()
                  .filter(s -> s.startsWith("b"))
                  .count();

6. Sorting a list of strings:

List<String> words = Arrays.asList("foo", "bar", "baz", "qux");
List<String> sortedWords = words.stream()
                                .sorted()
                                .collect(Collectors.toList());

7. Grouping a list of numbers by their remainder when divided by a certain value:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
Map<Integer, List<Integer>> groupedNumbers = numbers.stream()
                                                    .collect(Collectors.groupingBy(n -> n % 3));

8. Joining a list of strings into a single string:

List<String> words = Arrays.asList("foo", "bar", "baz", "qux");
String joinedWords = words.stream()
                          .collect(Collectors.joining(", "));

9. Finding the first element in a list that matches a certain condition:

List<String> words = Arrays.asList("foo", "bar", "baz", "qux");
Optional<String> firstWord = words.stream()
                                  .filter(s -> s.length() > 3)
                                  .findFirst();

10. Finding the first element in a list that matches a certain condition:

List<String> words = Arrays.asList("foo", "bar", "baz", "qux");
Optional<String> firstWord = words.stream()
                                  .filter(s -> s.length() > 3)
                                  .findFirst();

11. Finding the distinct elements in a list:

List<Integer> numbers = Arrays.asList(1, 2, 3, 2, 4, 3, 5, 4, 6, 5, 7, 6, 8, 7, 9, 8, 10);
List<Integer> distinctNumbers = numbers.stream()
                                       .distinct()
                                       .collect(Collectors.toList());

12. Counting frequency of elements in a list:

List<Integer> numbers = Arrays.asList(1, 2, 3, 2, 4, 3, 5, 4, 6, 5, 7, 6, 8, 7, 9, 8, 10);
Map<Integer, Long> frequency = numbers.stream().collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));