import java.util.concurrent.CountDownLatch;

/**
 * Created by cute coder
 * 2021/9/5 13:14
 */
public class CountDownLatchDemo {
    public static void main(String[] args) throws Exception{
        CountDownLatch countDownLatch = new CountDownLatch(6);
        for (int i = 0; i < 6; i++) {
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName() + "\t 上完自习，离开教室");
                countDownLatch.countDown();
            }, String.valueOf(i)).start();
        }
        countDownLatch.await();
        System.out.println(Thread.currentThread().getName() + "\t ***********班长最后关门走人");
    }

    public static void closeDoor() throws InterruptedException{


    }
}

输出

0	 上完自习，离开教室
1	 上完自习，离开教室
2	 上完自习，离开教室
3	 上完自习，离开教室
4	 上完自习，离开教室
5	 上完自习，离开教室
main	 ***********班长最后关门走人

加枚举灭六国

import lombok.Getter;

/**
 * Created by cute coder
 * 2021/9/5 13:31
 */
public enum CountryEnum {
    ONE(1,"齐"),TWO(2,"楚"),THREE(3,"燕"),FOUR(4,"赵"),FIVE(5,"魏"),SIX(6,"韩");
    @Getter private Integer retCode;
    @Getter private String retMessage;

    CountryEnum(Integer retCode, String retMessage) {
        this.retCode = retCode;
        this.retMessage = retMessage;
    }
    public static CountryEnum forEach_CountryEnum(int index){
        CountryEnum[] myArray = CountryEnum.values();
        for (CountryEnum element : myArray) {
            if (index == element.getRetCode()) {
                return element;
            }
        }
        return null;
    }
}

main

public class CountDownLatchDemo {
    public static void main(String[] args) throws Exception{
        CountDownLatch countDownLatch = new CountDownLatch(6);
        for (int i = 1; i <= 6; i++) {
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName() + "\t 国，被灭");
                countDownLatch.countDown();
            }, CountryEnum.forEach_CountryEnum(i).getRetMessage()).start();
        }
        countDownLatch.await();
        System.out.println(Thread.currentThread().getName() + "\t ***********秦帝国");
    }

    public static void closeDoor() throws InterruptedException{


    }
}