SemaphoreExample.java

package com.example.demo;

import java.util.concurrent.Semaphore;

public class SemaphoreExample {

    private static final Semaphore PARKING = new Semaphore(3);

    public static void main(String[] args) throws InterruptedException {
        for (int i = 1; i <= 9; i++) {
            new Car(i).start();
            Thread.sleep(i * 100L);
        }
    }

    static class Car extends Thread {

        private int number;

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

        @Override
        public void run() {
            try {
                System.out.println(number + " car is arrived");
                Thread.sleep(1000L);
                PARKING.acquire();
                System.out.println(number + " car is parked");
                Thread.sleep(3000L);
                PARKING.release();
                System.out.println(number + " car is left");
            } catch (InterruptedException ignored) {
            }
        }
    }


}