用于多线程下的StringBuffer和StringBuilder的状态

package org.donkey.app.StringBufferAndStringBuilder;import java.util.concurrent.CountDownLatch;/** * Created with IntelliJ IDEA. * User: Donkey * Date: 13-11-24 * Time: 上午11:28 * 用于多线程下的StringBuffer和StringBuilder的状态， * 其实有人说StringBuffrer是线程安全的而StringBuilder是线程不安全的，这种说法是错误的 * 这中线程安全是相对的，在StringBuffer中大部分方法都加上了synchronized关键字，使得同一时刻，不会两个线程 * 同时访问该方法，但在一个线程不安去的环境下用StringBuffer去工作,得到的结果也不一定和预期的一样，就如同本例。 * 它们的本质的区别在于：StringBuffer的结果与预期不一样是因为逻辑代码的问题，不存在多个线程同时访问而产生未知的 * 数据问题。而StringBuilder是有可能在同一时刻被多个线程所访问而产生线程同步问题 */public class StringBufferAndStringBuilder {    public static void main(String[] args){        long startTime = System.currentTimeMillis();        StringBuffer sb = new StringBuffer();        StringBuilder sbd = new StringBuilder();        int threadNum = 1000; //线程数        //定义正在运行的线程数        CountDownLatch runningThreadNum = new CountDownLatch(threadNum);        System.out.println(Thread.currentThread().getName()+"-start");        //创建多个子线程        for(int i = 0; i < threadNum; i++){            new ThreadTest(sb, runningThreadNum).start();        }        //等待子线程都执行完了再执行主线程剩下的动作        try {            runningThreadNum.await();            System.out.println(sb.toString());            System.out.println(Thread.currentThread().getName()+"-end");            long endTime = System.currentTimeMillis();            System.out.println("runningTime:"+(endTime-startTime));        } catch (InterruptedException e) {            e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.        }    }}class ThreadTest extends Thread{    private StringBuffer sbd;    //子线程记数器,记载着运行的线程数    private CountDownLatch runningThreadNum;    public  ThreadTest(StringBuffer sbd, CountDownLatch runningThreadNum){        super();        this.sbd = sbd;        this.runningThreadNum = runningThreadNum;    }    @Override    public void run(){        System.out.println(Thread.currentThread().getName()+"-start");        for (int i = 0; i < 10; i++){              if(i == 5){                  try {                      Thread.sleep(200);                  } catch (InterruptedException e) {                      e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.                  }              }            sbd.append(i);        }        System.out.println(Thread.currentThread().getName()+"-end");        runningThreadNum.countDown();    }}