ArrayList线程不安全测试

在jdk的介绍中，ArrayList是线程不安全的，指的是多线程情况下会有多个线程同时访问这个对象，导致数据达不到预期。

以下是一个示例：

public class ArrayListUnsyncTest {

private static List list = new ArrayList() ;

public static void main (String[] args) {

( new ArrayListUnsyncTest()).test() ;

}

private void test (){

int threadCount = 1000 ;

CountDownLatch countDownLatch = new CountDownLatch(threadCount) ;

ExecutorService exec = Executors. newFixedThreadPool (threadCount) ;

for ( int i= 0 ; i<threadCount ; i++){

exec.submit( new WorkerRunanble(countDownLatch , String. valueOf (i))) ;

}

try {

countDownLatch.await() ;

} catch (InterruptedException e) {

e.printStackTrace() ;

}

exec.shutdown() ;

//System.out.println(list);

System. out .println( list .size()) ;

}

class WorkerRunanble extends Thread{

CountDownLatch countDownLatch ;

String name ;

public WorkerRunanble (CountDownLatch countDownLatch , String name){

this . countDownLatch = countDownLatch ;

this . name = name ;

}

@Override

public void run () {

List list1 = new ArrayList() ;

for ( int j= 0 ; j< 10 ; j++){

list1.add( name + "_" +j) ;

}

list .addAll(list1) ;

countDownLatch .countDown() ;

}

}

}

这个例子中，最终list的size大小可能不是1000*10这么大，原因是多个线程同时往里面写值，造成数据被覆盖。