线程不安全的ArrayList

概述

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java.util.ArrayList不是线程安全的，当有多个线程并发读写ArrayList的时候，ArrayList会抛出如下异常

java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:819)
    at java.util.ArrayList$Itr.next(ArrayList.java:791)

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代码演示

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import java.util.List;

public class ReadThread implements Runnable{
private List<String> list ;
public ReadThread(List<String> list) {
this.list = list;
    }

@Override
public void run() {
for(String ele : list) {
          System.out.println(ele);
      }
    }
}

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import java.util.List;

public class WriteThread implements Runnable{
private List<String> list ;
public WriteThread(List<String> list) {
this.list = list;
    }

@Override
public void run() {
this.list.add("11");
    }
}

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import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ArrayListConCurrentWriteReadTest {

private void test() {
//1、准备数据
List<String> list = new ArrayList<>();
list.add("1");
list.add("2");
list.add("3");
list.add("4");
list.add("5");

//2、模拟多线程对list进行读和写
        ExecutorService executorService = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 5; i++) {
            executorService.execute(new ReadThread(list));
            executorService.execute(new WriteThread(list));
        }
    }


public static void main(String[] args) {
 new ArrayListConCurrentWriteReadTest().test();
 }
}

运行上面的代码就会抛出java.util.ConcurrentModificationException