Не понимаю, почему не проходит

package com.javarush.task.task16.task1612; /* Stopwatch (Секундомер) */ public class Solution { public static volatile boolean isStopped = false; public static void main(String[] args) throws InterruptedException { Runner ivanov = new Runner("Ivanov", 6); Runner petrov = new Runner("Petrov", 8); //на старт! //внимание! //марш! ivanov.start(); petrov.start(); Thread.sleep(2000); isStopped = true; Thread.sleep(1000); } public static class Stopwatch extends Thread { private Runner owner; private int stepNumber; public Stopwatch(Runner runner) { this.owner = runner; } public void run() { try { while (!isStopped) { doStep(); } } catch (InterruptedException e) { e.printStackTrace(); } } private void doStep() throws InterruptedException { stepNumber++; Thread.sleep(1000 / owner.getSpeed()); System.out.println(owner.getName() + " делает шаг №" + stepNumber + "!"); } } public static class Runner { Stopwatch stopwatch; private String name; private int speed; public Runner(String name, int speed) { this.name = name; this.speed = speed; this.stopwatch = new Stopwatch(this); } public String getName() { return name; } public int getSpeed() { return speed; } public void start() { stopwatch.start(); } } }