日后整理
1 import java.math.BigInteger; 2 3 public class Factorial { 4 5 public static void main(String[] args) { 6 // System.out.println(recursion(0)); 7 // System.out.println(circulation(1)); 8 System.out.println(bigInteger(100)); 9 } 10 11 /** 12 * 方法一 迭代实现阶乘 13 */ 14 public static int recursion(int n) { 15 int sum = 1; 16 if (n < 0) 17 throw new IllegalArgumentException("必须为正整数"); 18 if (n == 1 || n == 0) { 19 return sum; 20 } else { 21 sum = n * recursion(n - 1); 22 return sum; 23 } 24 // return sum; 25 26 } 27 28 /** 29 * 方法二 循环实现阶乘 30 */ 31 public static int circulation(int n) { 32 int sum = 1; 33 if (n >= 0) { 34 if (n == 0 || n == 1) { 35 return 1; 36 } else { 37 int i = 1; 38 while (i <= n) { 39 sum = sum * n; 40 n--; 41 } 42 return sum; 43 } 44 } else 45 throw new IllegalArgumentException("传入参数非法！"); 46 // return sum; 47 } 48 49 /** 50 * 方法三 利用BigInteger类 51 */ 52 53 public static BigInteger bigInteger(int n) { 54 BigInteger sum = new BigInteger("1"); 55 if (n >= 0) { 56 if (n == 0 || n == 1) { 57 return BigInteger.valueOf(1); 58 } else { 59 int i = 1; 60 while (i <= n) { 61 sum = sum.multiply(BigInteger.valueOf(n)); 62 n--; 63 } 64 return sum; 65 } 66 } else 67 throw new IllegalArgumentException("传入参数非法！"); 68 } 69 70 }
http://ly5633.iteye.com/blog/1219408