import java.util.concurrent.*; public class SemaphoreCounter { public static void main(String[] args) throws InterruptedException { SemaphoreCounter sc = new SemaphoreCounter(); Counter counter = new Counter(); Thread thread1 = new Thread(new Logic(counter)); Thread thread2 = new Thread(new Logic(counter)); thread1.start(); thread2.start(); thread1.join(); thread2.join(); } } public class Logic implements Runnable { private Counter counter; public Logic(Counter counter) { this.counter = counter; } @Override public void run() { while (true) { System.out.println(Thread.currentThread() + ":" + counter.increment()); try { Thread.sleep((int) (Math.random() * 1000)); } catch (InterruptedException e) { e.printStackTrace(); } } } } public class Counter { private int counter = 0; private Semaphore semaphore = new Semaphore(1); public int increment() { int val = 0; try { semaphore.acquire(); } catch (InterruptedException e) { e.printStackTrace(); } val = counter++; semaphore.release(); return val; } }