java - 我的倒计时只减 1 就不再减了，这是为什么？

Question

所以，我想在服务类中为用户输入的日期创建一个倒计时。现在我在倒计时方面遇到了问题。似乎无论如何它只减去 1 秒并且不会进一步。这是代码:

倒计时的逻辑

package com.example.service;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public class CounterService {
    LocalDateTime dateTime;

    public LocalDateTime getDateTime(){
        return dateTime;
    }

    public void setDateTime(LocalDateTime dateTime) {
        this.dateTime = dateTime;
    }

    public LocalDateTime parseDate(String eventDate) {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
        dateTime = LocalDateTime.parse(eventDate, formatter);
        return dateTime;
    }


    public static void main(String[] args) {

        CounterService cs = new CounterService();
        LocalDateTime a = LocalDateTime.of(2021,11,11,21,43,44);
        cs.setDateTime(a);

        Runnable r = new Counter(cs);
        new Thread(r).start();

    }
}

和可运行的

package com.example.service;

import java.time.LocalDateTime;

public class Counter implements Runnable {
    CounterService counter;

    public Counter(CounterService cs) {
        this.counter = cs;
    }

    public void setCounter(CounterService cs) {
        this.counter = cs;
    }

    public void run() {
        LocalDateTime countFromThisDate = counter.getDateTime();
        try {
            boolean x = true;
            while (x) {
                LocalDateTime substracting = countFromThisDate.minusSeconds(1);
                Thread.sleep(1000);
                System.out.println(substracting);
            }
        } catch (InterruptedException ex) {
            ex.printStackTrace();
        }
    }
}

另外，我如何添加这个计数器(在它工作后)，以便它动态刷新并逐一减去每一秒？

Answer 1

这里声明一个实现缺陷 - Thread.sleep 不能保证线程在耗时间隔后运行，它只是在时间间隔后使线程状态准备(由 cpu 运行) 。相反，您应该使用系统时间来获取自计数器启动以来耗时。

--更新--

对 CounterService 进行一点小改动即可完成工作。除了倒计时日期时间之外，CounterService 还将保留一个开始时间。代码如下所示 -

class CounterService {      

    private LocalDateTime dateTime;

    private LocalDateTime startTime;

    public CounterService(LocalDateTime dateTime, LocalDateTime startTime) {
        this.dateTime = dateTime;
        this.startTime = startTime;
    }

    public LocalDateTime getCounterTime() {
        return dateTime.minusSeconds(startTime.until(LocalDateTime.now(), ChronoUnit.SECONDS));
    }

    public static void main (String[] args) throws java.lang.Exception {
        LocalDateTime a = LocalDateTime.of(2021,11,11,21,43,44);
        LocalDateTime startTime = LocalDateTime.now();

        final CounterService counterService = new CounterService(a, startTime);

        new Thread(() -> {
            while (true) {
                System.out.println(counterService.getCounterTime());
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }
}