CountDownLatch 倒数的门栓 

1. CountDownLatch latch = new CountDownLatch(threads.length);  创建一个门栓,在门栓上面记个数
2. 每一个线程结束就countDown 
3. 开启线程
4. latch.await();   每一个线程结束后线程数减一，当 latch.await()为0的时候门栓就打开

package com.mashibing.juc.c_020;import java.util.concurrent.CountDownLatch;public class T06_TestCountDownLatch {public static void main(String[] args) {usingJoin();usingCountDownLatch();}private static void usingCountDownLatch() {Thread[] threads = new Thread[100];//创建一个门栓在门栓上面记个数CountDownLatch latch = new CountDownLatch(threads.length);for(int i=0; i<threads.length; i++) { //每一个线程结束就countDownthreads[i] = new Thread(()->{int result = 0;for(int j=0; j<10000; j++) result += j;latch.countDown();});}//线程开启for (int i = 0; i < threads.length; i++) {threads[i].start();}try { //门栓，拴住不动latch.await();  } catch (InterruptedException e) {e.printStackTrace();}System.out.println("end latch");}private static void usingJoin() {Thread[] threads = new Thread[100];for(int i=0; i<threads.length; i++) {threads[i] = new Thread(()->{int result = 0;for(int j=0; j<10000; j++) result += j;});}for (int i = 0; i < threads.length; i++) {threads[i].start();}for (int i = 0; i < threads.length; i++) {try {threads[i].join();} catch (InterruptedException e) {e.printStackTrace();}}System.out.println("end join");}
}