Java8的新特性与案例解析&stream流使用场景[转]

https://blog.csdn.net/weixin_44107140/article/details/129721852
https://blog.csdn.net/weixin_35754962/article/details/129076624
https://blog.csdn.net/The_clown/article/details/113339283

package top.irun2u.test;

import java.time.*;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.OptionalInt;
import java.util.stream.Collectors;

/**
 * @Author: haifei
 * @Date: 2023/9/13 16:18
 */
public class J8Test {

    public static void main(String[] args) {
        newDateTime();
        newStream();
        lambdaSort();
        lambdaThread();
    }

    public static void newDateTime() {
        System.out.println(LocalDate.now());
        System.out.println(LocalTime.now());
        System.out.println(LocalDateTime.now());
        System.out.println(Instant.now()); //时间戳

//        LocalDateTime dateTime1 = LocalDateTime.of(2021, 1, 1, 0, 0, 0);
//        LocalDateTime dateTime2 = LocalDateTime.now();
//        Duration duration = Duration.between(dateTime1, dateTime2);
//        System.out.println("时间间隔: " + duration);
//
//        LocalDate date1 = LocalDate.of(2021, 1, 1);
//        LocalDate date2 = LocalDate.now();
//        Period period = Period.between(date1, date2);
//        System.out.println("日期间隔: " + period);
    }

    public static void newStream() {
        //1.过滤
        List<String> names = Arrays.asList("Tom", "Jerry", "Alice", "Bob", "Jack");
        List<String> result = names.stream().filter(name -> name.startsWith("J")).collect(Collectors.toList());
        System.out.println(result); // 输出 [Jerry, Jack]

        //2.映射
        List<Integer> nums = Arrays.asList(1, 2, 3, 4, 5);
        List<Integer> squares = nums.stream().map(num -> num * num).collect(Collectors.toList());
        System.out.println(squares); // 输出 [1, 4, 9, 16, 25]

        //3.排序
        List<String> names2 = Arrays.asList("Tom", "Jerry", "Alice", "Bob", "Jack");
        List<String> result2 = names2.stream().sorted().collect(Collectors.toList());
        System.out.println(result2); // 输出 [Alice, Bob, Jack, Jerry, Tom]

        //4.统计
        List<Integer> nums2 = Arrays.asList(1, 2, 3, 4, 5);
        long count = nums2.stream().count();
        int sum = nums2.stream().mapToInt(Integer::intValue).sum();
        OptionalInt max = nums2.stream().mapToInt(Integer::intValue).max();
        System.out.println("count: " + count + ", sum: " + sum + ", max: " + max.getAsInt());
        // 输出 count: 5, sum: 15, max: 5

        //5.匹配
        List<Integer> nums3 = Arrays.asList(1, 2, 3, 4, 5);
        boolean allMatch = nums3.stream().allMatch(num -> num > 0);
        boolean anyMatch = nums3.stream().anyMatch(num -> num > 3);
        boolean noneMatch = nums3.stream().noneMatch(num -> num > 5);
        System.out.println("allMatch: " + allMatch + ", anyMatch: " + anyMatch + ", noneMatch: " + noneMatch);
        // 输出 allMatch: true, anyMatch: true, noneMatch: true

        //6.规约
        List<Integer> nums4 = Arrays.asList(1, 2, 3, 4, 5);
        int sum4 = nums4.stream().reduce(0, (acc, num) -> acc + num);
        Optional<Integer> product = nums4.stream().reduce((acc, num) -> acc * num);
        System.out.println("sum: " + sum4 + ", product: " + product.orElse(0));
        // 输出 sum: 15, product: 120
    }

    public static void lambdaSort() {
        List<Integer> numbers = Arrays.asList(3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5);
        List<Integer> sortedNumbers = numbers
                .stream()
                .sorted((a, b) -> a.compareTo(b))
                .collect(Collectors.toList());
        System.out.println(sortedNumbers); 
        // [1, 1, 2, 3, 3, 4, 5, 5, 5, 6, 9]
    }

    public static void lambdaThread() {
        Runnable task = () -> {
            System.out.println("Hello, world!");
        };
        new Thread(task).start();
        //Hello, world!
    }

}

对象列表抽取属性成新的列表

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