集合类不安全

1.ArrayList

    import java.util.*;import java.util.concurrent.CopyOnWriteArrayList;//ConcurrentModificationException并发修改异常public class ListTest {public static void main(String[] args) {//并发下ArrayList安全吗？/*** 解决方案* 1.List<String> list=new Vector<>();     Vector的add方法底层使用的是Synchronized* 2.List<String> list= Collections.synchronizedList(new ArrayList<>());* 3.List<String> list=new CopyOnWriteArrayList<>();  CopyOnWriteArrayList的add方法底层使用的是Lock，效率更高*//*** CopyOnWrite写入时复制，COW 计算机程序设计领域的一种优化策略*///List<String> list=new Vector<>();//List<String> list= Collections.synchronizedList(new ArrayList<>());List<String> list=new CopyOnWriteArrayList<>();for (int i = 0; i < 10; i++) {new Thread(()->{list.add(UUID.randomUUID().toString().substring(0,5));System.out.println(list);},String.valueOf(i)).start();}}}

2.HashSet

    import java.util.Collections;import java.util.HashSet;import java.util.Set;import java.util.UUID;import java.util.concurrent.CopyOnWriteArraySet;//ConcurrentModificationException:并发修改异常public class HashSetTest {public static void main(String[] args) {//HashSet<String> set = new HashSet<>();/***解决方案：* 1.Set<String> set= Collections.synchronizedSet(new HashSet<>());* 2.Set<String> set=new CopyOnWriteArraySet<>();*/Set<String> set=new CopyOnWriteArraySet<>();for (int i = 0; i < 30; i++) {new Thread(()->{set.add(UUID.randomUUID().toString().substring(0,5));System.out.println(set);},String.valueOf(i)).start();}}}

3.HashMap

    import java.util.HashMap;import java.util.Map;import java.util.UUID;import java.util.concurrent.ConcurrentHashMap;//ConcurrentModificationException:并发修改异常public class HashMapTest {public static void main(String[] args) {//线程不安全//Map<String,String> map=new HashMap<>();Map<String,String> map= new ConcurrentHashMap<>();for (int i = 0; i < 30; i++) {new Thread(()->{map.put(Thread.currentThread().getName(), UUID.randomUUID().toString().substring(0,5));System.out.println(map);},String.valueOf(i)).start();}}}