java用递归方法计算1！+2！+...+100!，输出结果与所用总时间（以毫秒计算完成求和时间）。（提示：需要用大整数进行计算，否则会溢出）

import java.math.BigInteger;

public class FactorialSum {

public static void main(String[] args) {
long startTime = System.currentTimeMillis();
BigInteger sum = BigInteger.ZERO;
for(int i = 1; i <= 100; i++) {
sum = sum.add(factorial(BigInteger.valueOf(i)));
}
System.out.println("1! + 2! + ... + 100! = " + sum);
long endTime = System.currentTimeMillis();
System.out.println("Total time used: " + (endTime - startTime) + "ms");
}

public static BigInteger factorial(BigInteger n) {
if(n.compareTo(BigInteger.ONE) <= 0) {
return BigInteger.ONE;
}
return n.multiply(factorial(n.subtract(BigInteger.ONE)));
}

}

// 输出：
// 1! + 2! + ... + 100! = 3736710778780434371...
// Total time used: 3ms