Stream流式编程用例

Stream流式编程用例：

filter, map, flatmap, limit, skip, sort, distinct, collect, reduce, summary statistics

public class StreamTest {

    public static void main(String[] args) {
        //filter
        Stream<Integer> stream = Stream.of(1, 2, 3, 4, 5);
        Stream<Integer> filteredStream = stream.filter(n -> n % 2 == 0); // 过滤出偶数
//        filteredStream.forEach(System.out::println);

        //map
        Stream<String> stream2 = Stream.of("apple", "banana", "cherry");
        Stream<Integer> mappedStream = stream2.map(String::length); // 映射为单词长度
//        mappedStream.forEach(System.out::println);

        //flatmap
        List<List<Integer>> nestedList = Arrays.asList(
                Arrays.asList(1, 2),
                Arrays.asList(3, 4),
                Arrays.asList(5, 6)
        );
        Stream<Integer> flattenedStream = nestedList.stream().flatMap(List::stream);
//        flattenedStream.forEach(System.out::println);

        //limit
        Stream<Integer> stream3 = Stream.of(1, 2, 3, 4, 5);
        Stream<Integer> limitedStream = stream3.limit(3); // 只保留前 3 个元素
//        limitedStream.forEach(System.out::println);

        //skip
        Stream<Integer> stream4 = Stream.of(1, 2, 3, 4, 5);
        Stream<Integer> skippedStream = stream4.skip(2); // 跳过前 2 个元素
//        skippedStream.forEach(System.out::println);

        //sort
        Stream<Integer> stream5 = Stream.of(5, 2, 4, 1, 3);
        Stream<Integer> sortedStream = stream5.sorted(); // 自然顺序排序
//        sortedStream.forEach(System.out::println);

        //distinct
        Stream<Integer> stream6 = Stream.of(1, 2, 2, 3, 3, 3);
        Stream<Integer> distinctStream = stream6.distinct(); // 去重
//        distinctStream.forEach(System.out::println);

        //collect
        Stream<String> stream7 = Stream.of("apple", "banana", "cherry");
        List<String> collectedList = stream7.toList(); // 收集为 List
//        collectedList.forEach(System.out::println);

        //reduce 规约
        Stream<Integer> stream8 = Stream.of(1, 2, 3, 4, 5);
        Optional<Integer> sum = stream8.reduce(Integer::sum); // 对所有元素求和
//        System.out.println("sum: " + sum);

        //summary statistics
        IntStream stream9 = IntStream.of(1, 2, 3, 4, 5);
        IntSummaryStatistics stats = stream9.summaryStatistics();
        System.out.println("Count: " + stats.getCount());
        System.out.println("Min: " + stats.getMin());
        System.out.println("Max: " + stats.getMax());
        System.out.println("Sum: " + stats.getSum());
        System.out.println("Average: " + stats.getAverage());
    }
}