9.18

import java.util.Timer;
import java.util.TimerTask;

int countdownSeconds = 10; // 倒计时
        Timer timer = new Timer();
        TimerTask task = new TimerTask() {
            int remainingSeconds = countdownSeconds;
            public void run() {
                if (remainingSeconds == 0) {
                    System.out.println("倒计时结束，时间到");
                    System.exit(0); // 结束程序
                } else {
                    remainingSeconds--;
                }
            }
        };