public static class Clock extends Thread {
        private int seconds;

        @Override
        public void run() {
            try {
                while (!currentThread().isInterrupted()) {
                    Thread.sleep(1000);
                    seconds++;
                    System.out.println(seconds);
                }
            } catch (InterruptedException e) {
                System.out.println("Конец отсчета.");
            }
        }
    }

public static void main(String[] args) throws InterruptedException {
        Clock clock = new Clock();
        clock.start();
        Thread.sleep(5000);
        clock.interrupt();

seconds++;
System.out.println(seconds);