基于BigInteger的多线程计算阶乘的各位数字和

import java.math.BigInteger;
import java.util.ArrayList;
import java.util.IntSummaryStatistics;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
import java.util.stream.Collector;
import java.util.stream.Collectors;

class FactorialSum implements Callable<BigInteger> {
    private int startNumber;
    private int endNumber;
    public FactorialSum(int startNumber, int endNumber) {
        this.startNumber = startNumber;
        this.endNumber = endNumber;
    }
    public BigInteger factorial() {
        BigInteger factorialResult = new BigInteger("1");
        BigInteger bigIntegerEnd=new BigInteger(String.valueOf(endNumber));
        int count=endNumber-startNumber;
        BigInteger step=new BigInteger("1");
        while (count>=0){
            factorialResult=factorialResult.multiply(bigIntegerEnd);
            bigIntegerEnd=bigIntegerEnd.subtract(step);
            count--;
        }
        return factorialResult;
    }
    @Override
    public BigInteger call() throws Exception {
        return factorial();
    }
    public static String factorialSum(String number) {
        char[] chars = number.toCharArray();
        List<Integer> list = new ArrayList<Integer>();
        for (int i = 0; i < chars.length; i++) {
            list.add(chars[i] - '0');
        }
        return String.valueOf(list.stream().collect(Collectors.summarizingInt(m -> m)).getSum());
    }
    public static String createThread(int number) throws ExecutionException, InterruptedException {
        if (number >= 50) {
            int average = number / 4;
            FutureTask<BigInteger> thread1 = new FutureTask<BigInteger>(new FactorialSum(1, average));
            new Thread(thread1).start();
            FutureTask<BigInteger> thread2 = new FutureTask<BigInteger>(new FactorialSum(average + 1, average * 2));
            new Thread(thread2).start();
            FutureTask<BigInteger> thread3 = new FutureTask<BigInteger>(new FactorialSum(average * 2 + 1, average * 3));
            new Thread(thread3).start();
            FutureTask<BigInteger> thread4 = new FutureTask<BigInteger>(new FactorialSum(average * 3 + 1, number));
            new Thread(thread4).start();
            return thread1.get().multiply(thread2.get()).multiply(thread3.get()).multiply(thread4.get()).toString();
        } else {
            FutureTask<BigInteger> thread1 = new FutureTask<BigInteger>(new FactorialSum(1, number));
            new Thread(thread1).start();
            return thread1.get().toString();
        }

    }

}

public class Main {

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        long startTime = System.currentTimeMillis();
        System.out.println(FactorialSum.factorialSum(FactorialSum.createThread(Integer.valueOf(args[0]))));
        System.out.println("times:" + (System.currentTimeMillis() - startTime));
    }
}

运行结果如下：

image.png