Fork/Join实例

来源：互联网发布：seo推广编辑：程序博客网时间：2024/06/04 20:11

（1）含返回值

问题：1+2+...+100

1.思路

分解为1+2,3+4,，...99+100，然后对这50个结果进行求和

2.任务实现

import java.util.concurrent.ExecutionException;import java.util.concurrent.RecursiveTask;public class CalculateTask extends RecursiveTask<Integer>{//因为需要返回值，所以使用RecursiveTaskprivate static final long serialVersionUID = -8486729149866588744L;private static final int THRESHOLD = 2;// 阈值private int start;private int end;public CalculateTask(int start, int end) {        this.start = start;        this.end = end;    }@Overrideprotected Integer compute() {int sum = 0;if (end-start<THRESHOLD) {//分解为2个数的和然后计算for(;start<=end;start++){sum += start;}}else {int mid = (start + end) >>> 1;    RecursiveTask<Integer> task1 = new CalculateTask(start, mid);    RecursiveTask<Integer> task2 = new CalculateTask(mid+1, end);    invokeAll(task1,task2);        try {sum = task1.get()+task2.get();} catch (InterruptedException e) {e.printStackTrace();} catch (ExecutionException e) {e.printStackTrace();}}return sum;}}

3.测试

package com.test;import java.util.concurrent.ExecutionException;import java.util.concurrent.ForkJoinPool;import java.util.concurrent.Future;import org.junit.Test;public class QuickSortTest {@Testpublic void test(){ForkJoinPool forkJoinPool = new ForkJoinPool();// 生成一个计算任务，负责计算1+2+3+4CalculateTask task = new CalculateTask(1, 4);// 执行一个任务Future<Integer> result = forkJoinPool.submit(task);forkJoinPool.shutdown();try {System.out.println(result.get());} catch (InterruptedException e) {e.printStackTrace();} catch (ExecutionException e) {e.printStackTrace();}}}

（2）无返回值

问题：快排

1.思路

根据中间值分解为2个区间，然后区间内再执行

2.任务实现

import java.util.concurrent.RecursiveAction;public class CalculateTask extends RecursiveAction{//这里不需要返回值，所以使用RecursiveActionprivate static final long serialVersionUID = 2476846494375574971L;private int[] number = {};private int begin;private int end;private static final int THRESHOLD = 1;// 阈值public QuickSortTask(int[] number,int begin, int end){this.number = number;this.begin = begin;this.end = end;}@Overrideprotected void compute() {if (end-begin<THRESHOLD) {//只有一个数，那么不用排序了return;}else{int mid = adjust(number,begin,end);QuickSortTask task1 = new QuickSortTask(number,begin, mid - 1);QuickSortTask task2 = new QuickSortTask(number,mid + 1, end);invokeAll(task1, task2);}}private int adjust(int[] a, int begin, int end) {int flag = a[begin];while (begin<end) {while (a[end]>=flag && begin<end) end--;if (begin<end) a[begin] = a[end];while (a[begin]<=flag && begin<end) begin++;if (begin<end)a[end] = a[begin];}a[begin] = flag;return begin;}}

3.测试

import java.util.concurrent.ExecutionException;import java.util.concurrent.ForkJoinPool;import java.util.concurrent.Future;import java.util.concurrent.TimeUnit;import org.junit.Test;public class QuickSortTest {@Testpublic void test() {ForkJoinPool forkJoinPool = new ForkJoinPool();int[] a = {54,12,36,16,96,62};QuickSortTask task = new QuickSortTask(a,0, 5);// 执行一个任务forkJoinPool.submit(task);while(!task.isDone()){        }for (int i : a) {System.out.print(i+" ");}forkJoinPool.shutdown();}}

0 0