Объясните пожалуйста

public class Solution {
    public static void main(String[] args) throws IOException {
        InputStreamReader in = new InputStreamReader(System.in);
        BufferedReader reader = new BufferedReader(in);
        //create and run thread
        Stopwatch stopwatch = new Stopwatch();
        stopwatch.start();
        //read a string
        reader.readLine();
        stopwatch.interrupt();
        //close streams
        reader.close();
        in.close();
    }

    public static class Stopwatch extends Thread {
        private int seconds;



        public void run() {

           while (!currentThread().isInterrupted()) {

               try {
                   seconds++;
                   Thread.sleep(1000);
                   //add your code here - добавьте код тут
               } catch (InterruptedException e) {
                   System.out.println(seconds);
               }
           }
        }
    }
}