题目不清楚，是多个线程同时打印倒计时，还是各个线程自己打印自己的倒计时？关键就是同步而已

import java.util.Date;
public class Sample {
    public static void main(String[] args) {
        Runnable r = new Runnable() { //多线程同时打印一个倒计时
            int seconds = 30; //倒计30秒
            public void run() {
                int current = seconds;
                while (current > 0) {
                    try {
                        synchronized(this) {
                            if (current == seconds) {
                                Date d = new Date();
                                System.out.printf("%s:倒数%d秒, time:%tT\n",
                                        Thread.currentThread().getName(), current, d);
                                seconds--;
                            }
                            current = seconds;
                        }
                        Thread.sleep(1000);
                        synchronized(this) {
                            if (current == 0) {
                                System.out.printf("%s:倒计时结束。\n", Thread.currentThread().getName());
                            }
                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }
        };
        for (int i=0; i<10; i++) { //多线程同时打印一个倒计时
            new Thread(r).start();
        }

        /* 多线程各自打印自己的倒计时
        Object locker = new Object();
        for (int i=0; i<10; i++) {
            new Thread() {
                int seconds = 30;
                public void run() {
                    while (seconds > 0) {
                        try {
                            synchronized(locker) {
                                Date d = new Date();
                                System.out.printf("%s:倒数%d秒, time:%tT\n",
                                        Thread.currentThread().getName(), seconds--, d);
                            }
                            Thread.sleep(1000);
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }
                    System.out.printf("%s:倒计时结束。\n", Thread.currentThread().getName());
                }
            }.start();
        }
        */
    }
}

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高分悬赏：Java语言多线程倒计时怎么同步输出，怎么用多线程来实现

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