理论：
CountDownLatch是一个非常实用的多线程控制工具类。常用的就下面几个方法：
代码语言：javascript复制CountDownLatch(int count) //实例化一个倒计数器，count指定计数个数
countDown() // 计数减一
await() //等待，当计数减到0时，所有线程并行执行未使用CountDownLatch的代码：
代码语言：javascript复制public class Demo {
public static void main(String[] args) {
for (int i = 0; i < 5; i ) {
new Thread(()->{
System.out.println(Thread.currentThread().getName() "t 工作任务完成，离开公司");
},String.valueOf(i)).start();
}
System.out.println(Thread.currentThread().getName() "t 最后将公司门锁死，离开公司");
}
}控制台：
使用CountDownLatch的代码：
代码语言：javascript复制public class Demo {
public static void main(String[] args) throws Exception{
CountDownLatch countDownLatch = new CountDownLatch(5);
for (int i = 0; i < 5; i ) {
new Thread(()->{
System.out.println(Thread.currentThread().getName() "t 工作任务完成，离开公司");
countDownLatch.countDown();
},String.valueOf(i)).start();
}
countDownLatch.await();
System.out.println(Thread.currentThread().getName() "t 最后将公司门锁死，离开公司");
}
}控制台：
案例二：
代码语言：javascript复制package tst.project;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class Test {
public static void main(String[] args) {
int tasks = 3;
final CountDownLatch latch = new CountDownLatch(tasks);
ExecutorService executorService = Executors.newFixedThreadPool(tasks);
executorService.submit(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("5秒完成：" latch);
latch.countDown();
}
});
executorService.submit(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("3秒完成：" latch);
latch.countDown();
}
});
executorService.submit(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("1秒完成：" latch);
latch.countDown();
}
});
executorService.shutdown();
try {
latch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}控制台：
结合下一章阅读：https://blog.csdn.net/java_wxid/article/details/99170471
