How do I use CountDownLatch in Java?

How do I use CountDownLatch in Java?

CountDownLatch is a synchronization aid that allows one or more threads to wait until a set of operations being performed in other threads completes.

Can you give me a code example?

Sure! Here's a simple example:

import java.util.concurrent.CountDownLatch;

public class CountDownLatchExample {
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch latch = new CountDownLatch(3);

        for (int i = 0; i < 3; i++) {
            new Thread(new Worker(latch)).start();
        }

        latch.await(); // Wait until the count reaches zero
        System.out.println("All workers finished!");
    }

    static class Worker implements Runnable {
        private final CountDownLatch latch;

        Worker(CountDownLatch latch) {
            this.latch = latch;
        }

        public void run() {
            try {
                // Simulate work
                Thread.sleep((long) (Math.random() * 1000));
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            } finally {
                latch.countDown(); // Decrement the count
            }
        }
    }
}

What happens if I call countDown() more times than the initial count?

If you call countDown() more times than the initial count, it won't throw an exception, but the count will remain at zero. The latch will stay in a state where any subsequent calls to await() will return immediately.