Development Chaos Theory » Blog Archive » How (not) to write Factorial in Java.

I will admit this post was inspired by How would you write factorial(n) in java? So excuse me while I rant in code: I have a point to make at the bottom of this article.

Now most people who write factorial in Java may start with something simple, like:

public static int factorial(int n)    {        if (n == 0) return 1;        return n * factorial(n-1);    }

Wrapping this in a class (since we’re talking about Java, of course), they may write it inside a utility class. For example:

public class FactorialUtil{    public static int factorial(int n)    {        if (n == 0) return 1;        return n * factorial(n-1);    }}

Simple, no?

There is a non-recursive solution as well:

public class FactorialUtil{    public static int factorial(int n)    {        int ret = 1;        for (int i = 1; i <= n; ++i) ret *= i;        return ret;    }}

Now the observent reader may note “gosh, it’s entirely possible the value will be longer than an integer”, so they’ll perhaps rewrite in terms of BigInteger or at least in terms of long, depending on the requirements of the program. Thus:

...

Very funny. And, unfortunately, very true.