1 普通方式

package org.test;

public class FactorialExample {
    
    public static long factorialIterative(int n) {
        // 处理边界情况
        if (n < 0) {
            throw new IllegalArgumentException("阶乘只能计算非负整数");
        }
        
        long result = 1;
        for (int i = 1; i <= n; i++) {
            result *= i;
        }
        return result;
    }
    
    public static void main(String[] args) {
        int number = 5;
        long result = factorialIterative(number);
        System.out.println("使用循环计算 " + number + "! = " + result);
    }
}

2 递归方式

package org.test;

public class FactorialExample {
    
    public static long factorialRecursive(int n) {
        // 处理边界情况
        if (n < 0) {
            throw new IllegalArgumentException("阶乘只能计算非负整数");
        }
        
        // 基本情况：0! = 1
        if (n == 0) {
            return 1;
        }
        
        // 递归调用
        return n * factorialRecursive(n - 1);
    }
    
    public static void main(String[] args) {
        int number = 5;
        long result = factorialRecursive(number);
        System.out.println("使用递归计算 " + number + "! = " + result);
    }
}