CountDownLatch是一个Java的并发工具类，用于使一个线程等待其他线程完成各自的工作。其主要用法如下：
-
创建一个CountDownLatch实例，指定初始计数器的值。
| CountDownLatch countDownLatch = new CountDownLatch(3); |
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在需要等待的线程中调用await()方法，该方法会阻塞当前线程，直到计数器减到0。
| countDownLatch.await(); |
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在其他线程中，每次完成一项工作后，调用countDown()方法来减少计数器的值。
| countDownLatch.countDown(); |
当所有线程都完成了各自的工作后，计数器减为0，此时等待的线程会从await()方法返回，继续执行后续代码。
以下是一个简单的示例代码：
java复制代码| public class CountDownLatchExample { | |
| public static void main(String[] args) throws InterruptedException { | |
| CountDownLatch countDownLatch = new CountDownLatch(3); | |
| Thread thread1 = new Thread(() -> { | |
| System.out.println("Thread 1 started"); | |
| try { | |
| Thread.sleep(1000); | |
| } catch (InterruptedException e) { | |
| e.printStackTrace(); | |
| } | |
| System.out.println("Thread 1 finished"); | |
| countDownLatch.countDown(); | |
| }); | |
| Thread thread2 = new Thread(() -> { | |
| System.out.println("Thread 2 started"); | |
| try { | |
| Thread.sleep(2000); | |
| } catch (InterruptedException e) { | |
| e.printStackTrace(); | |
| } | |
| System.out.println("Thread 2 finished"); | |
| countDownLatch.countDown(); | |
| }); | |
| Thread thread3 = new Thread(() -> { | |
| System.out.println("Thread 3 started"); | |
| try { | |
| Thread.sleep(3000); | |
| } catch (InterruptedException e) { | |
| e.printStackTrace(); | |
| } | |
| System.out.println("Thread 3 finished"); | |
| countDownLatch.countDown(); | |
| }); | |
| thread1.start(); | |
| thread2.start(); | |
| thread3.start(); | |
| countDownLatch.await(); // 等待所有线程完成工作后返回继续执行后续代码... | |
| } | |
| } |