分支合并例子

/*** 計(jì)算1+2+3...+100 ， 拆分成多任務(wù)計(jì)算，最后匯總，拆分標(biāo)準(zhǔn)是最大最小值差值不超過(guò)10* 如果任務(wù)比較耗時(shí)，明顯多線程拆分要快得多*/ class MyTask extends RecursiveTask<Integer> {//拆分最大最小差值不超過(guò)10private static final Integer VALUE = 10;private int begin; //拆分開(kāi)始值private int end; //拆分結(jié)束值private int result;//返回結(jié)果//創(chuàng)建有參構(gòu)造public MyTask(int begin, int end){this.begin = begin;this.end = end;}//拆分合并過(guò)程@Overrideprotected Integer compute() {//判斷相加的兩個(gè)數(shù)差值是否大于10if((end - begin) <= VALUE) {//相加操作for(int i = begin; i <= end; i++) {result += i;try {TimeUnit.MICROSECONDS.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}}}else {//進(jìn)一步拆分//二分拆分int mid = (begin + end) / 2;//拆分左邊MyTask task01 = new MyTask(begin, mid);;//拆分右邊MyTask task02 = new MyTask(mid + 1, end);//調(diào)用方法拆分task01.fork();task02.fork();//合并結(jié)果result = task01.join() + task02.join();}return result;} }public class ForkJoinDemo {public static void main(String[] args) throws ExecutionException, InterruptedException {long start = System.currentTimeMillis();//創(chuàng)建MyTask對(duì)象MyTask myTask = new MyTask(0,100);//創(chuàng)建分鐘合并池對(duì)象ForkJoinPool forkJoinPool = new ForkJoinPool();ForkJoinTask<Integer> forkJoinTask = forkJoinPool.submit(myTask);//獲取最終合并之后的結(jié)果Integer result = forkJoinTask.get();System.out.println("result = " + result);//關(guān)閉池對(duì)象forkJoinPool.shutdown();long end = System.currentTimeMillis();System.out.println("花費(fèi)時(shí)間：" + (end - start));int sum = 0;for (int i = 0; i <= 100; i++) {sum += i;TimeUnit.MICROSECONDS.sleep(100);}System.out.println("sum = " + sum);long end2 = System.currentTimeMillis();System.out.println("花費(fèi)時(shí)間：" + (end2 - end));} }

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