CountDownLatchExample.java

package com.example.demo;

import java.util.concurrent.CountDownLatch;

public class CountDownLatchExample {

    private static final CountDownLatch START = new CountDownLatch(5);

    public static void main(String[] args) throws InterruptedException {
        System.out.println("Waiting 5 cars appearing to the start line");

        for (int i = 1; i <= 5; i++) {
            new Car(i).start();
        }

        START.await();
        System.out.println("START!");
    }

    static class Car extends Thread {

        private int number;

        Car(int number) {
            this.number = number;
        }

        @Override
        public void run() {
            try {
                Thread.sleep(number * 1000L);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(number + " car is ready to start");
            START.countDown();
        }
    }
}