[Java知识库]JDK 8 ArrayList并发问题

• jdk8 ArrayList在并发添加元素的情况下，会丢元素和出现null的情况

public class Test {

    private static List list = new ArrayList<>();

    @SneakyThrows
    public static void main(String[] args) {
        testArrayList();
    }
    
    private static void testArrayList() throws InterruptedException {
        CountDownLatch latch = new CountDownLatch(2);
        // 线程1 => t1
        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 100_0000; i++) {
                    list.add("thread1_" +  i);
                    if (i%10_0000==0) {
                        System.out.println("thread1 put 10W");
                    }
                }
                System.out.println("thread1 end");
                latch.countDown();
            }
        },"thread one").start();
        // 线程2 => t2
        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 100_0000; i++) {
                    list.add("thread2_" +  i);
                    if (i%10_0000==0) {
                        System.out.println("thread2 put 10W");
                    }
                }
                System.out.println("thread2 end");
                latch.countDown();
            }
        },"thread tow").start();
        latch.await();

        //期望集合大小应该为200W，实际会小于200W，并且会出现null元素
        System.out.println("集合的大小："+list.size()+"，null元素的数量："+list.parallelStream().filter(Objects::isNull).count());
    }
}