ArryList集合
多线程下不安全;可能会报错:java.util.ConcurrentModificationException(并发修改异常)
import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;
//java.util.ConcurrentModificationException 并发修改异常
public class ListTest {
public static void main(String[] args) {
//并发下ArrayList是不安全的
List<Object> list = new ArrayList<>();
//CopyOnWrite 写入时复制 COW 计算机程序应用领域的一种优化策略
//多个线程调用的时候,list,读取的时候,固定的,写入(覆盖)
//在写入的时候避免覆盖,造成数据问题
for (int i = 1; i <= 10; i++) {
new Thread(()->{
list.add(UUID.randomUUID().toString().substring(0,5));
System.out.println(list);
}).start();
}
}
}
解决方案:
- List<String> list = new Vector<>();
- List<String> strings = Collections.synchronizedList(new ArrayList<>());
- List<String> strings = new CopyOnWriteArrayList<>();
概念:CopyOnWrite写入时复制,计算机程序设计语言的一种优化策略。(保证效率和性能问题)
import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;
//java.util.ConcurrentModificationException 并发修改异常
public class ListTest {
public static void main(String[] args) {
//并发下ArrayList是不安全的
/**
* 解决方案:
* 1.List<Object> list = new Vector<>();
* 2.List<Object> list = new Vector<>();
* 3.List<Object> list = Collections.synchronizedList(new ArrayList<>());
* 4.List<Object> list = new CopyOnWriteArrayList<>();
*/
// List<Object> list = new ArrayList<>();
// List<Object> list = new Vector<>();
// List<Object> list = Collections.synchronizedList(new ArrayList<>());
//CopyOnWrite 写入时复制 COW 计算机程序应用领域的一种优化策略
//多个线程调用的时候,list,读取的时候,固定的,写入(覆盖)
//在写入的时候避免覆盖,造成数据问题
List<Object> list = new CopyOnWriteArrayList<>();
for (int i = 1; i <= 10; i++) {
new Thread(()->{
list.add(UUID.randomUUID().toString().substring(0,5));
System.out.println(list);
}).start();
}
}
}
HashSet集合
多线程下不安全;可能会报错:java.util.ConcurrentModificationException(并发修改异常)
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import java.util.UUID;
import java.util.concurrent.CopyOnWriteArraySet;
//java.util.ConcurrentModificationException
public class SetList {
public static void main(String[] args) {
HashSet<Object> set = new HashSet<>();
for (int i = 1; i <=10 ; i++) {
new Thread(()->{
set.add(UUID.randomUUID().toString().substring(0,5));
System.out.println(set);
},String.valueOf(i)).start();
}
}
}
解决方案:
- Set<String> strings = Collections.synchronizedSet(new HashSet<>());
- Set<String> strings = new CopyOnWriteArraySet<>();
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import java.util.UUID;
import java.util.concurrent.CopyOnWriteArraySet;
//java.util.ConcurrentModificationException
/**
* 解决方案
* 1.Set<Object> set = Collections.synchronizedSet(new HashSet<>());
* 2.Set<Object> set = new CopyOnWriteArraySet<>();
*/
public class SetList {
public static void main(String[] args) {
// HashSet<Object> set = new HashSet<>();
// Set<Object> set = Collections.synchronizedSet(new HashSet<>());
Set<Object> set = new CopyOnWriteArraySet<>();
for (int i = 1; i <=13 ; i++) {
new Thread(()->{
set.add(UUID.randomUUID().toString().substring(0,5));
System.out.println(set);
},String.valueOf(i)).start();
}
}
}
hashset集合的底层是hashmap的key
HashMap集合
多线程下不安全;可能会报错:java.util.ConcurrentModificationException(并发修改异常)
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
public class MapTest {
public static void main(String[] args) {
//hashmap默认值 new Hashmap<>(16,0.75);
Map<String, String> map = new HashMap<>();
for (int i = 1; i <= 10; i++) {
new Thread(()->{
map.put(Thread.currentThread().getName(), UUID.randomUUID().toString().substring(0,5));
System.out.println(map);
},String.valueOf(i)).start();
}
}
}
解决方案:
- Map<String, String> concurrentHashMap = new ConcurrentHashMap<>();
- Map<String, String> map = Collections.synchronizedMap(new HashMap<>());
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
public class MapTest {
public static void main(String[] args) {
//hashmap默认值 new Hashmap<>(16,0.75);
// Map<String, String> map = new HashMap<>();
// Map<String, String> map = Collections.synchronizedMap(new HashMap<>());
ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>();
for (int i = 1; i <= 10; i++) {
new Thread(()->{
map.put(Thread.currentThread().getName(), UUID.randomUUID().toString().substring(0,5));
System.out.println(map);
},String.valueOf(i)).start();
}
}
}