集合不安全

• Arraylist线程不安全，add方法没有锁
• 会出现ConcurrentModificationException()异常
• vector线程安全,但是并发性下降

Arraylist出现异常

public class test07 {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();

        for (int i = 1;i<=30;i++){
            new Thread(() -> {
                list.add(UUID.randomUUID().toString().substring(0,8));
                System.out.println(list);
            },String.valueOf(i)).start();

        }
    }
}

• 解决方法：

1. new Vector()<>;
2. Collections.synchronizedList(new ArrayList<>());
3. CopyOnWriteArrayList<>();读写分离

public class test07 {
    public static void main(String[] args) {
        List<String> list = Collections.synchronizedList(new ArrayList<>());
		 List<String> list = new CopyOnWriteArrayList<>();

        for (int i = 1;i<=30;i++){
            new Thread(() -> {
                list.add(UUID.randomUUID().toString().substring(0,8));
                System.out.println(list);
            },String.valueOf(i)).start();

        }
    }
}