一些列表类及其特性
| 类 | 线程安全 | Iterator | 特性 | 说明 |
| Vector | 是 | fail-fast | 内部方法用synchronized修饰，因此执行效率较低 |
1. 线程安全的列表类并不意味着调用它的代码就一定线程安全 2. 只有CopyOnWriteArrayList能支持在遍历时修改列表元素 |
| ArrayList | 否 | fail-fast | 在多线程环境中使用不当易出错 | |
| Collections.synchronizedList | 是 | fail-fast | Collections.synchronizedList可以得到线程安全的列表，与Vector类似 | |
| CopyOnWriteArrayList | 是 | fail-safe | 每个线程先复制一份并把地址指向新list，在新的list上操作，因此最终结果未必符合预期，适用于经常需要读但很少修改的场景 |
以下代码模拟多线程环境下，各个类Iterator机制的表现
package com.concurrent.test; import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Vector;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CountDownLatch; /**
* 多线程操作列表
*/
public class ThreadListTest { public void multipleThreadArrayList(final List<Integer> list) throws InterruptedException {
int count = 10;
for (int i = 0; i < count; i++) {
list.add(i);
} final CountDownLatch countDownLatch = new CountDownLatch(2);
new Thread(new Runnable() { @Override
public void run() {
try {
Thread.sleep(1000);
} catch (InterruptedException e1) {
e1.printStackTrace();
} for (Integer integer : list) {
System.out.println(integer);
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
countDownLatch.countDown();
}
},"foreach-Thread").start(); new Thread(new Runnable() { @Override
public void run() {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("ThreadId:" + Thread.currentThread().getId() + " remove " + list.remove(0));
countDownLatch.countDown();
}
},"remove-Thread").start(); countDownLatch.await();
} public static void main(String[] args) throws InterruptedException {
ThreadListTest test = new ThreadListTest();
List<Integer> list ; list = new Vector<>();// Vector只保证内部方法线程安全
list = new ArrayList<>();// ArrayList效率比Vector高，但非线程安全
list = Collections.synchronizedList(new ArrayList<Integer>());// Collections.synchronizedList与Vector异曲同工
list = new CopyOnWriteArrayList<>();// CopyOnWriteArrayList线程安全：每个线程先复制一份并把地址指向新list，在新的list上操作，因此最终结果未必符合预期 test.multipleThreadArrayList(list);
System.out.println(list.toString()); } }