技術標籤：javajava演算法

計算10億之內所有的數之和：

三等：

   static void test() {
        long starttime = System.currentTimeMillis();
        long sum = 0;
        for (Long i = 0L; i < 1000000000L; i++) {
            sum += i;
        }
        long endtime = System.currentTimeMillis();
        System.out.println(endtime - starttime)
 
;// test();//4807

    }

六等：

public class ForkJoinTest extends RecursiveTask<Long> {


    private long start;
    private long end;
    private long temp = 10000L;
    private long sum;

    public ForkJoinTest(long start, long end) {
        this.start = start;
        this.end = end;
    }

    @Override
 

    protected Long compute() {
        if ((end - start) < temp) {
            for (Long i = start; i < end; i++) {
                sum += i;
            }
            return sum;
        } else {
            Long middle = (end + start) / 2;
            ForkJoinTest forkJoinTest = new ForkJoinTest
 
(start, middle);
            forkJoinTest.fork();
            ForkJoinTest forkJoinTest2 = new ForkJoinTest(middle + 1, end);
            forkJoinTest2.fork();

            return forkJoinTest.join() + forkJoinTest2.join();
        }
    }
}

    static void test2() throws ExecutionException, InterruptedException {
        long starttime = System.currentTimeMillis();

        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Long> forkJoinTest = new ForkJoinTest(0L, 1000000000L);
        ForkJoinTask<Long> submit = forkJoinPool.submit(forkJoinTest);
        Long aLong = submit.get();
        long endtime = System.currentTimeMillis();

        System.out.println(endtime - starttime);// test2();//4138

    }

九等：

 static void test3() {
        long starttime = System.currentTimeMillis();
        LongStream.rangeClosed(0L, 1000000000L).parallel().reduce(0, Long::sum);
        long endtime = System.currentTimeMillis();
        System.out.println(endtime - starttime);//test3（）//271

    }