编写一个示例程序，展示如何使用 CountDownLatch 类进行多线程同步和协作。

import java.util.concurrent.CountDownLatch;

public class CountDownLatchExample {
    public static void main(String[] args) {
        // 创建 CountDownLatch，计数器初始值为 3，表示需要等待 3 个线程完成任务
        CountDownLatch latch = new CountDownLatch(3);

        // 创建并启动 3 个工作线程
        for (int i = 1; i <= 3; i++) {
            int threadNumber = i; // 用于线程标识
            new Thread(() -> {
                try {
                    System.out.println("Worker " + threadNumber + " is working...");
                    Thread.sleep((long) (Math.random() * 3000)); // 模拟任务执行时间
                    System.out.println("Worker " + threadNumber + " has finished.");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    latch.countDown(); // 每个线程完成任务后，计数器减 1
                }
            }).start();
        }

        // 主线程等待所有工作线程完成任务
        try {
            System.out.println("Main thread is waiting for workers to finish...");
            latch.await(); // 等待计数器归零
            System.out.println("All workers have finished. Main thread resumes.");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

import java.util.concurrent.CountDownLatch;

public class CountDownLatchRaceExample {
    public static void main(String[] args) {
        CountDownLatch readyLatch = new CountDownLatch(1); // 控制选手开始的信号
        CountDownLatch finishLatch = new CountDownLatch(3); // 等待所有选手完成

        // 创建并启动 3 个选手线程
        for (int i = 1; i <= 3; i++) {
            int threadNumber = i;
            new Thread(() -> {
                try {
                    System.out.println("Runner " + threadNumber + " is ready...");
                    readyLatch.await(); // 等待发令信号
                    System.out.println("Runner " + threadNumber + " started running!");
                    Thread.sleep((long) (Math.random() * 3000)); // 模拟跑步时间
                    System.out.println("Runner " + threadNumber + " finished!");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    finishLatch.countDown(); // 每个选手跑完后，计数器减 1
                }
            }).start();
        }

        try {
            Thread.sleep(1000); // 模拟准备时间
            System.out.println("Ready... Set... Go!");
            readyLatch.countDown(); // 发令信号，所有线程开始运行
            finishLatch.await(); // 等待所有选手完成
            System.out.println("All runners have finished the race!");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}