2019独角兽企业重金招聘Python工程师标准>>> 
package cm.concurrent;
import java.util.concurrent.CountDownLatch;
public class UseContDownLatch {
public static void main(String[] args) {
//2表示唤醒的次数，如果没有达到唤醒的次数，countDownLatch.await();之后的业务将无法执行！
final CountDownLatch countDownLatch = new CountDownLatch(2);
Thread t1=new Thread(new Runnable() {
@Override
public void run() {
try {
System.out.println("进入t1线程,等待其他线程处理完成.........");
countDownLatch.await();
System.out.println("t2和t3初始化完成,t1才能线程继续执行.................");
} catch (Exception e) {
e.printStackTrace();
}
}
},"t1");
Thread t2=new Thread(new Runnable() {
@Override
public void run() {
try {
System.out.println("进入t2线程进行初始化.........");
Thread.sleep(3000);
System.out.println("t2说：t1线程可以继续执行.................");
//第一次唤醒
countDownLatch.countDown();
} catch (Exception e) {
e.printStackTrace();
}
}
},"t2");
Thread t3=new Thread(new Runnable() {
@Override
public void run() {
try {
System.out.println("进入t3线程进行初始化.........");
Thread.sleep(4000);
System.out.println("t3说：t1线程可以继续执行.................");
//第二次唤醒
countDownLatch.countDown();
} catch (Exception e) {
e.printStackTrace();
}
}
},"t3");
t1.start();
t2.start();
t3.start();
}
}
确切的来说，第一次唤醒和第二次唤醒并不是绝对的，因为线程中每个线程争取cpu的先后顺序都书随机的，哪个先执行，哪个就是第一次唤醒。