CountDownLatch如何使用？

package constxiong.interview;

import java.util.concurrent.CountDownLatch;

/**
 * 测试使用100个线程，并发访问和等待多线程完成后处理
 * @author ConstXiong
 */
public class TestCountDownLatch2 {

    private static CountDownLatch cdl = new CountDownLatch(100);
    
    private static int count = 0;
    
    public static void main(String[] args) {
        testConcurrent();
//        testDoAfterOtherThreadComplete();
    }
    
    /**
     * 测试并发  do something...
     */
    private static void testConcurrent() {
        for (int i = 0; i < 100; i++) {
            //启动线程
            new Thread(() -> {
                try {
                    //当发令枪计数未减到 0 之前线程都会在此阻塞
                    cdl.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + ":" + System.currentTimeMillis() + " do something...");
            }).start();
            
            //发令枪计数减 1
            cdl.countDown();
        }
    }
    
    //测试等待多线程完成后处理
    private static void testDoAfterOtherThreadComplete() {
        //启动 100 个线程，对 count 递增
        for (int i = 0; i < 100; i++) {
            new Thread(() -> {
                count++;
                //发令枪计数减 1
                cdl.countDown();
            }).start();
        }
        
        try {
            cdl.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("main thread print count : " + count);
    }
    
}