递归因子方法返回一些负数

Question

这是我的阶乘方法:

public static long factorial(int num1) {
    if (num1 <= 1) 
        return 1; 
    else
        return num1 * factorial(num1 - 1);
}

这就是所谓的递归因子方法:

for (i = 0; i <= 25; i++)
    System.out.printf  ("%d !=  %,d\n", i, factorial (i));

到目前为止一切顺利,输出看起来似乎是正确的,但是一些因子是负的而不是正的:

OUTPUT:
0 !=  1
1 !=  1
2 !=  2
3 !=  6
4 !=  24
5 !=  120
6 !=  720
7 !=  5,040
8 !=  40,320
9 !=  362,880
10 !=  3,628,800
11 !=  39,916,800
12 !=  479,001,600
13 !=  6,227,020,800
14 !=  87,178,291,200
15 !=  1,307,674,368,000
16 !=  20,922,789,888,000
17 !=  355,687,428,096,000
18 !=  6,402,373,705,728,000
19 !=  121,645,100,408,832,000
20 !=  2,432,902,008,176,640,000
21 !=  -4,249,290,049,419,214,848
22 !=  -1,250,660,718,674,968,576
23 !=  8,128,291,617,894,825,984
24 !=  -7,835,185,981,329,244,160
25 !=  7,034,535,277,573,963,776

21,22和24是否定的,为什么会这样？这是某种"除以0"悖论吗？

Answer 1

你满满的多了.您需要根据包含long值的二进制数来考虑它.只要将长度可以包含的最大正值加1,它就会滚动到负最小值.

您可能希望阅读本文以获得完整的理解. http://en.wikipedia.org/wiki/Two%27s_complement

在Java中,您可以使用BigInteger获取更大的值 http://docs.oracle.com/javase/1.4.2/docs/api/java/math/BigInteger.html