阿里面试题

需求:
实现一个容器，提供两个方法，add，size,写两个线程，线程1添加10个元素到容器中，线程2实现监控元素的个数，当个数到5个时，线程2给出提示并结束

public class MyContainer3 {

    volatile List lists = new ArrayList<>();

    void add(Object obj){
        lists.add(obj);
    }

    int size(){
        return lists.size();
    }


    public static void main(String[] args) {
        MyContainer3 mc = new MyContainer3();

        CountDownLatch latch = new CountDownLatch(1);

        new Thread(() ->{
            System.out.println("t2启动");

            if (mc.size() != 5) {
                try {
                    latch.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println("t2结束");
        },"t2").start();


        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                mc.add(new Object());
                if (5 == mc.size()) {
                    latch.countDown();
                }
                System.out.println("count = " + mc.size());

                try {
                    TimeUnit.SECONDS.sleep(2);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"t1").start();



    }

}

结果:

image.png