面试题——在一个文本里有N多个数据，使用多线程最快求和

思路：把所有数据分组，每组使用一个线程去计算结果，计算完后再把结果汇总

具体实现如下：

1、用数据模拟文本里的数据

2、声明一个线程池和实现一个可返回结果的Callable接口

3、把果返回结果Future放到CopyOnWriteArrayList中用于结果集计算

4、此算法的缺点有待改进的地方是结果汇总时是被动去检测，而不是某个结果计算完成后主动去汇总，既然是分段计算，如果数据量足够大时，应该采用递归去实现分段汇总会更好

/** * Huisou.com Inc. * Copyright (c) 2011-2012 All Rights Reserved. */package thread;import java.util.List;import java.util.concurrent.Callable;import java.util.concurrent.CopyOnWriteArrayList;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Future;/** * @description *  * @author chenzehe * @email hljuczh@163.com * @create 2013-3-8 上午12:20:27 */public class CalculateTest {public static void main(String[] args) {int[] intNums = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 };System.out.println("Calculate start...");System.out.println("Calculate result:" + Calculate.calculate(intNums));System.out.println("Calculate finished.");}}class Calculate {static intpoolSize= 5;static ExecutorServiceexecutor= Executors.newFixedThreadPool(2);/** *  * @param targetNum * @return * @description 使用多线程对targetNum数组求和 * @author chenzehe * @todo */public static int calculate(int[] targetNum) {int result = 0;try {// 返回结果Future放到CopyOnWriteArrayList中用于结果集计算List<Future<Integer>> futures = new CopyOnWriteArrayList<Future<Integer>>();for (int i = 0; i < poolSize; i++) {// 提交任务futures.add(executor.submit(new CalculateCallable(targetNum, poolSize, i)));}// 等待返回结果while (true) {if (futures.size() == 0) {break;// 全部返回则跳出}for (Future<Integer> future : futures) {System.out.println("waiting...");if (future.isDone()) {result += future.get();futures.remove(future);// 有返回结果就移出}}}executor.shutdown();}catch (Exception ex) {ex.printStackTrace();}return result;}}class CalculateCallable implements Callable<Integer> {int[]targetNum;intthreadNum;intpoolSize;public CalculateCallable(int[] targetNum, int poolSize, int threadNum) {this.targetNum = targetNum;this.poolSize = poolSize;this.threadNum = threadNum;}@Overridepublic Integer call() {// 根据某种算法算出这里需要读取某部分数据，此处只是简单平均int result = 0;int eachSize = (targetNum.length + poolSize) / poolSize;int start = eachSize * threadNum;int end = start + eachSize;for (int i = start; i < end && i < targetNum.length; i++) {result += targetNum[i];}try {// 模拟长时间的运算Thread.sleep(3000);}catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}return result;}}

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1 楼 showtimes52007 2013-03-08 关于多线程更多的面试题,这篇文章有详细介绍:http://www.sujunqiang.com/archives/227.html