What is a semaphore in Java and how do I use it?

What is a semaphore in Java and how do I use it?

A semaphore in Java is a synchronization aid that controls access to a shared resource. It maintains a set of permits.

Can you give me an example of how to implement a semaphore?

Sure! Here's a simple example:

import java.util.concurrent.Semaphore;

public class SemaphoreExample {
    private static final Semaphore semaphore = new Semaphore(1);

    public static void main(String[] args) {
        Thread t1 = new Thread(() -> accessResource());
        Thread t2 = new Thread(() -> accessResource());
        t1.start();
        t2.start();
    }

    private static void accessResource() {
        try {
            semaphore.acquire();
            System.out.println(Thread.currentThread().getName() + " is accessing the resource.");
            Thread.sleep(2000); // Simulate resource access
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            semaphore.release();
            System.out.println(Thread.currentThread().getName() + " has released the resource.");
        }
    }
}

What happens if a thread tries to acquire a semaphore that is already taken?

If a thread tries to acquire a semaphore that is already taken, it will block and wait until a permit is released by another thread.