import java.math.BigInteger;

import java.util.concurrent.CountDownLatch;

public class MultiThreadedSum {

/**

* 多线程求1-1000w的和

* Create by mulin on 2021.03.08

*/

public static void main(String[] args) {

int num = 100; // 组数

int latchNum = 10000000 / 100; // 每组需要计算的数的个数

System.out.println("latchNum: " + latchNum);

BigInteger[] totalBI = new BigInteger[num];

// countdownlunch

CountDownLatch countDownLatch = new CountDownLatch(num);

for (int i = 0; i < num; i++) {

final int it = i;

new Thread(

() -> {

BigInteger multiply = new BigInteger(it * latchNum + 1 + "").add(new BigInteger((it + 1) * latchNum + "")).multiply(new BigInteger(latchNum / 2 + ""));

totalBI[it] = multiply;

countDownLatch.countDown();

}

).start();

}

try {

countDownLatch.await();

} catch (Exception e) {

e.printStackTrace();

} finally {

BigInteger bigInteger = new BigInteger("0");

for (BigInteger integer : totalBI) {

bigInteger = bigInteger.add(integer);

}

System.out.println("计算结果： " + bigInteger);

// 用通项式验证

System.out.println("直接计算结果： " +

new BigInteger("1").add(new BigInteger("10000000")).multiply(new BigInteger(10000000 / 2 + "")));

}

}

}