手动创建线程池，效果会更好哦。

确实，手动创建线程池可以更好地控制线程的数量和执行方式。以下是一个使用手动创建线程池的 CountDownLatch 示例：

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

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

        ExecutorService executor = createThreadPool(taskCount);

        for (int i = 0; i < taskCount; i++) {
            executor.submit(new Task(latch));
        }

        latch.await();
        System.out.println("All tasks have finished, now executing main task.");
        executor.shutdown();
    }

    static ExecutorService createThreadPool(int threadCount) {
        return Executors.newFixedThreadPool(threadCount);
    }

    static class Task implements Runnable {
        private CountDownLatch latch;

        public Task(CountDownLatch latch) {
            this.latch = latch;
        }

        @Override
        public void run() {
            try {
                System.out.println("Task started: " + Thread.currentThread().getName());
                Thread.sleep(1000);
                System.out.println("Task finished: " + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                latch.countDown();
            }
        }
    }
}

在这个例子中，我们通过 `createThreadPool()` 方法手动创建了一个固定大小的线程池，并将线程池作为参数传递给 `ExecutorService`。这样我们就可以更好地控制线程池的行为，例如指定线程池的大小等。其余部分的逻辑和之前的例子相同。