Java Stream API

Introduction

Java Are you using it! I often write something lately, but I feel that it has become quite convenient since the Stream API was implemented. Typical things like Stream.forEach and Stream.filter come out at once, Some things that I don't use often don't come out, so I'll keep them for memorandum.

Stream.generate Creates an unordered, infinite Stream. This is useful when creating irrelevant values, such as generating random numbers.

Document: docs

code

    public static void main(String[] args) {
        Stream<Double> stream = Stream.generate(() -> Math.random());
        stream.limit(5).forEach(System.out::println);
    }

result

0.022804976867977667
0.06422820749702451
0.7240936837411123
0.9070898332933144
0.6724389714182997

Stream.anyMatch With Predicate <T> as a parameter, true is returned if there is at least one value that matches the condition.

Documentation: docs

code

    public static void main(String[] args) {
        List<String> strList = Arrays.asList("dog", "cat", "bird");
        boolean match = strList.stream().anyMatch(e -> e.equals("dog"));
        System.out.println(match);
    }

result

true

Stream.allMatch With Predicate <T> as a parameter, true is returned if all the values match the conditions.

Documentation: docs

code

    public static void main(String[] args) {
        List<String> strList = Arrays.asList("dog", "cat", "bird");
        boolean match = strList.stream().allMatch(e -> e.equals("dog"));
        System.out.println(match);
    }

result

false

Stream.noneMatch With Predicate <T> as a parameter, it returns true if there is no value that matches the condition.

Documentation: docs

code

    public static void main(String[] args) {
        List<String> strList = Arrays.asList("dog", "cat", "bird");
        boolean match = strList.stream().noneMatch(e -> e.equals("fish"));
        System.out.println(match);
    }

result

true

Stream.takeWhile With Predicate <T> as a parameter, the value is returned while the conditions are met. In the example below, numbers less than 0 will be returned.

Document: docs

code

    public static void main(String[] args) {
        List<Integer> numList = Arrays.asList(
                -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5
        );
        numList.stream().takeWhile(x -> x < 0).forEach(System.out::println);
    }

result

-5
-4
-3
-2
-1

Stream.dropWhile With Predicate <T> as a parameter, the value is returned while the conditions are not met. In the example below, numbers greater than or equal to 0 will be returned.

Document: docs

code

    public static void main(String[] args) {
        List<Integer> numList = Arrays.asList(
                -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5
        );
        numList.stream().dropWhile(x -> x < 0).forEach(System.out::println);
    }

result

0
1
2
3
4
5

Finally

StreamAPI It's very convenient, isn't it? I would like to actively use it and aim for a code that can be understood intuitively. It ’s short, but that ’s it. Thank you very much!