证明HashSet、HashMap线程不安全、如何变成线程安全

（1）证明HashSet线程不安全

public static void main(String[] args) {Set<String> set = new HashSet<>();for (int i = 1; i <=30 ; i++) {new Thread(()->{set.add(UUID.randomUUID().toString().substring(0,8));System.out.println(set);},String.valueOf(i)).start();}}

（2）HashSet线程安全改造

Set<String> set = new CopyOnWriteArraySet<>();

（3）证明HashMap线程不安全

public static void main(String[] args) {Map<String,String> map = new HashMap<>();for (int i = 1; i <=30 ; i++) {new Thread(()->{map.put(Thread.currentThread().getName(),UUID.randomUUID().toString().substring(0,8));System.out.println(map);},String.valueOf(i)).start();}}

（4）HashMap线程安全改造

Map<String,String> map = new ConcurrentHashMap<>();