Java 实现阶乘 BigInteger

import java.math.BigInteger;

public class getFactorial {
    public static void main(String[] args) {
        // 15511210043330985984000000
        System.out.println(getFactorial("25").toString());
        // 9223372036854775807
        System.out.println(Long.MAX_VALUE);
    }
    
    public static BigInteger getFactorial(BigInteger num) {
        /**
         *    
         * 1  大于 1 才继续计算
         * 2 while 比 for 少点代码
         * 3 int long 范围有限
         * 4 递归浪费资源，深度太深jvm不支持，StackOverflowError
         * 5 使用更专业的计算包
         */
        BigInteger result = num;
        while(num.compareTo(BigInteger.ONE) > 0) {
            num = num.subtract(BigInteger.ONE);
            result = result.multiply(num);
        }
        return result;
    }
    
    public static BigInteger getFactorial(String numString) {
        return getFactorial(new BigInteger(numString));
    }
}