List 不安全
出现场景 ： 多线程环境下访问ArrayList
bug类型 ：
java.util.concurrent.CopyOnWriteArrayList–并发修改异常
- 解决方案
- new Vector()
- List arrayList = Collections.synchronizedList(new ArrayList<>())
- CopyonWriteArrayList arrayList1 = new CopyOnWriteArrayList<>()
package com.sydstart.unsafe;
import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;
public class ListTest {
public static void main(String[] args) {
// java.util.ConcurrentModificationException 并发修改异常
List arrayList = Collections.synchronizedList(new ArrayList<>());
CopyOnWriteArrayList
Set
- 总结：
解决方案
1.Set set = Collections.synchronizedSet(new HashSet());
2.CopyonWriteArraySet set01 = new CopyOnWriteArraySet<>();
package com.sydstart.unsafe;
import java.util.*;
import java.util.concurrent.CopyOnWriteArraySet;
public class SetTest {
public static void main(String[] args) {
Set set = Collections.synchronizedSet(new HashSet());
CopyOnWriteArraySet
HashMap不安全
package com.sydstart.unsafe;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Hashtable;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
public class MapTest {
public static void main(String[] args) {
ConcurrentHashMap hashMap= new ConcurrentHashMap<>();
Hashtable ht = new Hashtable<>();
// 方案一 : Collections.synchronizedMap(hashMap);
// 方案二 ：方案二 ：Hashtable hashTable= new Hashtable();
for (int i = 0; i < 10; i++) {
new Thread(()->{
int i1 =0;
ht.put(i1++ , UUID.randomUUID().toString().substring(0,5));
System.out.println(ht);
},"A").start();
}
for (int i = 0; i < 10; i++) {
new Thread(()->{
int i1 =0;
ht.put(i1++ , UUID.randomUUID().toString().substring(0,5));
System.out.println(ht);
},"B").start();
}
}
}
