想實現六個同學離開教室後，班長關門

錯誤寫法

public class CountDownLatchDemo {
    public static void main(String[] args) throws InterruptedException {
        for (int i = 1; i <=6; i++) {
            new Thread(()->{
                System.out.println(Thread.currentThread().getName()+"號同學離開教室了");
            },String.valueOf(i)).start();
        }
        System.out.println("班長鎖門了");
    }
}
 

效果如下

正確做法（countDownLatch)

import java.util.concurrent.CountDownLatch;
public class CountDownLatchDemo {
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch latch = new CountDownLatch(6);
        for (int i = 1; i <=6; i++) {
            new Thread(()->{
                System.out.println(Thread.currentThread().getName()+"號同學離開教室了");
                //計數 -1
                latch.countDown();
            },String.valueOf(i)).start();
        }
        //等待
        latch.await();
        System.out.println("班長鎖門了");
    }
}
 

效果如下