Runnable

定义作为一个团队需要完成的工作 Runnable .

Scheduled ExecutorService 要每隔一分钟左右运行一次,请检查当前日期与目标日期。如果倒计时已增加,则更新GUI中的显示。如果没有,什么也不做,让 可运行 再跑一分钟。

Oracle Tutorial on Executors .

ScheduledExecutorService ses = Executors.newSingleThreadScheduledExecutor();  // Use a single thread, as we need this to run sequentially, not in parallel.
ses.scheduleWithFixedDelay( r , 0L , 1L , TimeUnit.MINUTES ); // Pass the `Runnable`, an initial delay, a count to wait between runs, and the unit of time for those two other number arguments.

安排一次新的旅行会更有效率 可运行 每次,而不是自动重复,以便将延迟设置为直到下一个午夜的计算时间量。这样,遗嘱执行人就可以整天睡觉,而不是分秒必争。但是,如果用户的时钟更新到明显不同的当前时间,或者如果用户当前的默认时区发生变化(如果您依赖默认时区而不是明确设置默认时区),这种方法可能会失控。考虑到这一点 可运行

LocalDate

这个 LocalDate 类表示一个仅日期的值,该值不包含一天中的时间,也不包含 time zone offset-from-UTC .

Paris France Montréal Québec .

如果未指定时区,JVM将隐式应用其当前默认时区。这一违约可能会发生 change at any moment 在运行时(!),因此您的结果可能会有所不同。最好将所需/预期时区明确指定为参数。

指定一个 proper time zone name Continent/Region 例如 America/Montreal , Africa/Casablanca 或 Pacific/Auckland . 切勿使用2-4个字母的缩写,如 EST 或 IST 不 真正的时区,没有标准化,甚至不是唯一的(!)。

ZoneId z = ZoneId.of( "Asia/Kolkata" );  // Or ZoneId.systemDefault() to rely on the JVM’s current default time zone.
LocalDate today = LocalDate.now( z );

实例

这是一个完整的例子。有关详细信息,请搜索堆栈溢出。使用 ScheduledExecutorService 已经被报道过很多次了。

package work.basil.example;

import java.time.Instant;
import java.time.LocalDate;
import java.time.Month;
import java.time.ZoneId;
import java.time.temporal.ChronoUnit;
import java.util.Objects;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class DailyCountdown implements Runnable {
    private LocalDate dueDate;
    private Long daysRemaining;

    public DailyCountdown ( LocalDate dueDate ) {
        this.dueDate = dueDate;
    }

    @Override
    public void run () {
        try {
            System.out.println( "DEBUG - Running the DailyCountdown::run method at " + Instant.now() );
            ZoneId z = ZoneId.of( "America/Montreal" );  // Or ZoneId.systemDefault() to rely on the JVM’s current default time zone.
            LocalDate today = LocalDate.now( z );
            Long count = ChronoUnit.DAYS.between( today , this.dueDate );
            if ( Objects.isNull( this.daysRemaining ) ) {
                this.daysRemaining = ( count - 1 );
            }
            if ( this.daysRemaining.equals( count ) ) {
                // Do nothing.
            } else {
                // … Schedule on another thread for the GUI to update with the new number.
                this.daysRemaining = count;
            }
        } catch ( Exception e ) {
            // Log this unexpected exception, and notify sysadmin.
            // Any uncaught exception reaching the scheduled executor service would have caused it to silently halt any further scheduling.
        }
    }

    public static void main ( String[] args ) {
        // Put this code where ever appropriate, when setting up your GUI after the app launches.
        Runnable r = new DailyCountdown( LocalDate.of( 2018 , Month.FEBRUARY , 15 ) );
        ScheduledExecutorService ses = Executors.newSingleThreadScheduledExecutor();
        ses.scheduleWithFixedDelay( r , 0L , 1L , TimeUnit.MINUTES );

        // Be sure to gracefully shutdown the ScheduledExecutorService when your program is stopping. Otherwise, the executor may continue running indefinitely on the background thread.
        try {
            Thread.sleep( TimeUnit.MINUTES.toMillis( 7 ) ); // Sleep 7 minutes to let the background thread do its thing.
        } catch ( InterruptedException e ) {
            System.out.println( "The `main` thread was woken early from sleep." );
        }
        ses.shutdown();
        System.out.println( "App is exiting at " + Instant.now() ) ;
    }
}

for (LocalDate date = startDate; date.isBefore(endDate); date = date.plusDays(1))
{
    ...
}

你可以用 java.util.Timer 这门课。

FIVE_SECONDS_IN_MILLISECONDS 来测试程序。)

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Timer;
import java.util.TimerTask;

public class Scheduler {
  private static final long ONE_DAY_IN_MILLISECONDS = 1000 * 60 * 60 * 24;
  private static final long FIVE_SECONDS_IN_MILLISECONDS = 1000 * 5;

  public static void main(String[] args) {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

    TimerTask timerTask = new TimerTask() {
      @Override
      public void run() {
        Calendar c = Calendar.getInstance();
        String dateString = sdf.format(c.getTime());
        System.out.println(dateString);
        if (dateString.equals("2019-02-10")) {
          System.out.println("Date reached!");
        }
      }
    };

    Timer timer = new Timer();
    timer.schedule(timerTask, 0, ONE_DAY_IN_MILLISECONDS/*FIVE_SECONDS_IN_MILLISECONDS*/);
  }
}