請問ArrayList,HashSet,HashMap是線程安全的嗎?如果不是我想要線程安全的集合怎麼辦呢?
在集合中Vector 和HashTable是線程安全的,打開源碼發現其實就是把各自核心方法添加了synchornized關鍵字。
List<String> list = new ArrayList<>();//線程不安全
方法1:
List<String> list = new Vector<>();
方法2:
List<String> list = Collections.synchronizedList(new ArrayList<>());
方法3:
List<String> list = new CopyOnWriteArrayList<>();//寫時複製技術
Set<String> set = new CopyOnWriteArraySet<>();
Map<String,String> map = new ConcurrentHashMap<>();
package cn.zh.juc1205;
/**
* 1.故障現象
* Java.util.ConcurrentModificationException
* 2.導致原因
*
* 3.解決方法
* 3.1 new Vector<>()
* 3.2 Collections.synchronizedList(new ArrayList<>))
* 3.3 new CopyOnWriteArrayList()
* 4.優化建議(同樣的錯誤不犯第二次)
*
*/
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CopyOnWriteArraySet;
public class NotSafeDemo03 {
public static void main(String[] args) {
Map<String,String> map = new ConcurrentHashMap<>();
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();
}
}
public static void setNotSage(String[] args) {
Set<String> set = new CopyOnWriteArraySet<>();
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();
}
}
public static void listNodtSafe() {
// List<String> list = new ArrayList<>();
// List<String> list = new Vector<>();
// List<String> list = Collections.synchronizedList(new ArrayList<>());
//寫時複製技術
List<String> list = new CopyOnWriteArrayList<>();
/*list.add("a");
list.add("b");
list.add("c");
list.forEach(System.out::println);//方法引用*/
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();
}
}
}