error: multiply(long) is not public in BigInteger; cannot be accessed from outside package

Question

我正在尝试编写一个 Java 方法，该方法使用对 n 个不同对象按顺序排序的方法的数量进行计数 - 一种排列。每次我尝试编译我的代码时，我都会收到一条错误消息：

multiply(long) is not public in BigInteger; cannot be accessed from outside package.

我尝试用 fact = fact.multiply((long) i); 替换 fact = fact.multiply(i); 行，但也没有用。有人有什么想法吗？

import java.math.BigInteger;

public class Combinatorics  {

    public static void main(String[] args) {
        // 2.1
       System.out.println(CountPerm(9));

    }

    public static BigInteger CountPerm(int n) {
        BigInteger fact = BigInteger.valueOf((long) 1);
        for(int i = 1; i <= n; i++){
            fact = fact.multiply(i);
        }
        return fact;
    }
}

Answer 1

要乘以 BigIntegers，你需要给一个 BigInteger 参数，而不是 long 参数。方法是BigInteger.multiply(BigInteger).

将您的代码更改为：

fact = fact.multiply(BigInteger.valueOf(i));

旁注：

BigInteger.valueOf((long) 1); 应替换为 BigInteger.ONE。已经有一个预定义的常量。
一定要遵守 Java 命名约定：CountPerm 方法应该被称为 countPerm.

error: multiply(long) is not public in BigInteger; cannot be accessed from outside package

error: multiply(long) is not public in BigInteger; cannot be accessed from outside package

java

biginteger