Java流处理stream使用详解

public static void main(String[] args) {
    List<String> strings = new ArrayList<>();
    strings.add("asd");
    strings.add("asd");
    strings.add("qwe");
    List<String> names = strings.stream()
            // 过滤
            .filter(d -> {
                return d.contains("a");
            })
            // 去重
            .distinct()
            // 转换成列表
            .toList();
    for (String name : names) System.out.println(name); // 输出：asd
}

public static void main(String[] args) {
    List<Integer> numbers = Arrays.asList(1, 2, 3, 1, 2, 4, 2, 2);
    numbers.stream()
            .filter(i -> i % 2 == 0)
            .distinct()
            .forEach(System.out::println);
}

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

public static void main(String[] args) {
    List<Dish> dishes = new ArrayList<>();
    dishes.add(new Dish("apple", true, 120, Dish.Type.FRUIT));
    dishes.add(new Dish("pork", false, 900, Dish.Type.MEAT));
    dishes.add(new Dish("fish", false, 400, Dish.Type.FISH));
    List<String> dishNames = dishes.stream()
            .map(Dish::getName)
            .toList();
    dishes.forEach(System.out::println);
}

public static void main(String[] args) {
    // 创建单词表
    String[] words = {"goodbye", "hello", "night"};
    // 将单词表转换成流的形式
    Stream<String> swords = Arrays.stream(words);
    // 首先使用map，将所有字母都一一分割来开
    List<String> strings = swords.map(word -> word.split(""))
            // 使用扁平map，将提取到的字母装入一个流中
            .flatMap(Arrays::stream)
            // 字母去重
            .distinct()
            // 转换成列表
            .toList();
    strings.forEach(System.out::println);
}

public static void main(String[] args) {
    List<Dish> dishes = Menu.getMenu();
    if(dishes.stream().anyMatch(Dish::isVegetarian)){
        System.out.println("至少有一个素菜！");
    }
}

public static void main(String[] args) {
    List<Dish> dishes = Menu.getMenu();
    dishes.stream()
            .filter(Dish::isVegetarian)
            .findAny()
            .ifPresent(d -> System.out.println(d.getName()));
}

public static void main(String[] args) {
    int[] nums = {1, 2, 3, 4, 5};
    int sum = Arrays.stream(nums).sum();
    int sum2 = Arrays.stream(nums)
            .reduce(0, (a, b) -> a + b);
    int sum3 = Arrays.stream(nums)
            .reduce(0, Integer::sum);
}

public static void main(String[] args) {
    List<Dish> dishes = Menu.getMenu();
    int sum = dishes.stream()
            .mapToInt(Dish::getCalories)
            .sum();
}

IntStream is = dishes.stream().mapToInt(Dish::getCalories);
Stream<Integer> sis = is.boxed();

IntStream evenNumbers = IntStream.rangeClosed(1,100)
        .filter(n->n%2==0);
System.out.println(evenNumbers.count());