以计算0到1000之间的和为例

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;public class Main {
//求1~N全部整数的和，会上溢
int N = (int) 1e8;
int threadSize = 5;/*** 最原始最基础的方式：使用thread，自定义并发*/
class ThreadJoin {void go() {Thread[] a = new Thread[threadSize];//每个线程应该干多少活int per = (int) Math.ceil(N * 1.0 / a.length);final AtomicInteger s = new AtomicInteger(0);for (int i = 0; i < a.length; i++) {int ii = i;a[i] = new Thread(() -> {int sum = 0;for (int j = ii * per; j < Math.min(ii * per + per, N); j++) {sum += j;}s.addAndGet(sum);});a[i].start();}for (Thread i : a)try {i.join();} catch (InterruptedException e) {e.printStackTrace();}System.out.println(s.get() + " " + getClass().getName());}
}/*** 重量级的多线程框架：ThreadPoolExecutor，维护一个动态线程池*/
class UseThreadPoolExecutor {void go() {ThreadPoolExecutor executor = new ThreadPoolExecutor(threadSize, threadSize, 1, TimeUnit.SECONDS, new LinkedBlockingDeque<>());int per = (int) (Math.ceil(1.0 * N / threadSize));List<Future<Integer>> futureList = new LinkedList<>();for (int i = 0; i < threadSize; i++) {final int ii = i;futureList.add(executor.submit(() -> {int sum = 0;for (int j = ii * per; j < Math.min(N, ii * per + per); j++) {sum += j;}return sum;}));}int sum = 0;for (Future<Integer> j : futureList) {try {sum += j.get(Integer.MAX_VALUE, TimeUnit.SECONDS);} catch (Exception e) {e.printStackTrace();}}executor.shutdown();System.out.println(sum + " " + getClass().getName());}
}/*** ExecutorService：轻量级的线程池*/
class UseExecutorService {void go() {ExecutorService service = Executors.newFixedThreadPool(threadSize);int per = (int) (Math.ceil(N * 1.0 / threadSize));List<Future<Integer>> futureList = new LinkedList<>();for (int i = 0; i < threadSize; i++) {final int ii = i;futureList.add(service.submit(() -> {int sum = 0;for (int j = ii * per; j < Math.min(N, ii * per + per); j++) {sum += j;}return sum;}));}int sum = 0;for (Future<Integer> j : futureList) {try {sum += j.get(Integer.MAX_VALUE, TimeUnit.SECONDS);} catch (Exception e) {e.printStackTrace();}}service.shutdown();System.out.println(sum + " " + getClass().getName());}
}/*** 模拟Linux fork join操作*/class UseForkJoin {void go() {int per = (int) (Math.ceil(1.0 * N / threadSize));List<ForkJoinTask<Integer>> a = new ArrayList<>(threadSize);for (int i = 0; i < threadSize; i++) {final int ii = i;a.add(new RecursiveTask<Integer>() {@Overrideprotected Integer compute() {int sum = 0;for (int j = ii * per; j < Math.min(N, ii * per + per); j++) {sum += j;}return sum;}});a.get(i).invoke();}int s = 0;for (ForkJoinTask<Integer> i : a) {s += i.join();}System.out.println(s + " " + getClass().getName());}
}Main() {new ThreadJoin().go();new UseExecutorService().go();new UseThreadPoolExecutor().go();new UseForkJoin().go();
}public static void main(String[] args) {new Main();
}
}