CountDownLatch 示例

好的，这里是 CountDownLatch 的一个示例：

import java.util.concurrent.CountDownLatch;

public class CountDownLatchExample {
    public static void main(String[] args) throws InterruptedException {
        int numThreads = 5;
        CountDownLatch latch = new CountDownLatch(numThreads);

        for (int i = 0; i < numThreads; i++) {
            Thread thread = new Thread(() -> {
                System.out.println("Thread started: " + Thread.currentThread().getName());
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("Thread finished: " + Thread.currentThread().getName());
                latch.countDown();
            });
            thread.start();
        }

        latch.await();
        System.out.println("All threads finished.");
    }
}

这个示例创建了 5 个线程，每个线程都会打印出自己的名字，并且在执行完一些操作后调用 `countDown()` 方法。主线程调用 `await()` 方法等待所有线程执行完毕后输出 "All threads finished."。