java17Lambda expression and stream and multi-threading start

public static void main(String[] args) {
    
    
        IntStream isa = IntStream.range(1, 101);
        IntStream isb = IntStream.rangeClosed(1, 100);
        System.out.println(isa.sum());
        System.out.println(isb.sum());

        Stream<Integer> is = Stream.of(1, 2, 3, 4, 5, 6, 7, 8);
        //is.forEach(System.out::print);

        is.filter(e -> e % 2 == 0).forEach(e -> System.out.printf("%d ", e));
        System.out.println();
        System.out.println("=============");
        List<Integer> list = List.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
        System.out.println(list);
        Stream<Integer> s1 = list.stream();
        s1.forEach(e -> System.out.printf("%2d ", e));
        System.out.println();
        //并行流
        Stream<Integer> s2 = list.parallelStream();
        s2.forEach(e -> System.out.printf("%2d ", e));
        System.out.println("当前线程数" + Thread.activeCount());
        IntStream aa = Arrays.stream(new int[]{
    
    1, 2, 3, 4, 5, 6, 7, 8, 9}).parallel();
        aa.forEach(e -> System.out.printf("%2d ", e));
        System.out.println("当前线程数" + Thread.activeCount());
        //生成4个数，从1开始，依次加3
        Stream<Integer> ss1 = Stream.iterate(1, x -> x + 3).limit(4);
        ss1.forEach(e -> System.out.printf("%2d ", e));
        System.out.println();
        //生成10个随机小数
        Stream<Double> ss2 = Stream.generate(Math::random).limit(10);
        ss2.forEach(e -> System.out.printf("%.3f  ", e));
        System.out.println();
        Random r = new Random();
        IntStream ss3 = IntStream.generate(() -> r.nextInt(1, 101)).limit(10);
        ss3.forEach(e -> System.out.printf("%2d ", e));
        System.out.println();
        IntStream ss4 = IntStream.generate(() -> {
    
    
            Random rand = new Random();
            return rand.nextInt(1, 101);
        }).limit(10);
        ss4.forEach(e -> System.out.printf("%2d ", e));
        System.out.println();
        

    }
    

public static void main(String[] args) {
    
    

        //过滤
        IntStream ss1 = IntStream.range(1, 10);
        ss1.map(e -> e * e).forEach(e -> System.out.printf("%02d ", e));

        Stream<StudentA1> ss = Stream.of(
                new StudentA1(1, "张三", 58, "男"),
                new StudentA1(2, "张斯", 62, "男"),
                new StudentA1(3, "张当", 45, "女"),
                new StudentA1(4, "李书", 98, "男")
        );


        //Set<StudentA1> s1 = ss.collect(Collectors.toSet());
        //System.out.println(s1);


        //List<StudentA1> list = ss.toList();

        //List<String> listname = ss.map(StudentA1::getName).toList();
        //System.out.println(listname);
        System.out.println();

        int[] nn = {
    
    1, 2, 3, 4, 5};
        int sumnn = Arrays.stream(nn).sum();
        System.out.println(sumnn);

        //过滤
        ss.filter(e -> e.getSex().contains("男")).forEach(System.out::println);
    }
}

The list, set, and custom can be treated as a Stream stream.

3 ways to enable multithreading

Inherit the Thread class and rewrite the run method

class T1 extends Thread {
    
    
            @Override
            public void run() {
    
    
                System.out.println("hello t1");
            }
        }
        

use

var t1 = new T1();
        t1.start();
        

Implement the Runnable interface to implement the run method, and the object is used as the parameter of Thread

var t2 = new Thread(() -> {
    
    
            System.out.println("hello t2");
        }, "t2");
        t2.start();
        

Implement the Callable interface, and the object is used as the parameter of Thread. The multithreading of this method is mainly used to return the value.

 Callable<Integer> call = () -> {
    
    
            System.out.println("hello t3 返回10");
            return 10;
        };
        FutureTask<Integer> ft = new FutureTask<>(call);
        var t3 = new Thread(ft);
        t3.start();
        System.out.println(ft.get());