Using BigDecimal

Question

My factorial is hitting a wall, and it is a huge decimal (I put it under 1). How do I use BigDecimal? Here is what I am using to solve these factorials:
    public static double factorial(double n) {
        if      (n <  0)  throw new RuntimeException("Can't be negative stupid.");
        else if (n > 250) throw new RuntimeException("Number too big at the moment! :(");
        else if (n == 0)  return 1;
        else              return (1 / (n * factorial(n-1)));
double z = 200
factorial(z);I get errors because I don't think double can handle something so large. How do I change that snippet of code to BigDecimal, rather how do I use it? The API sort of tells me this is much different from regular number types. Also, can a BigDecimal have a value in the ones or tens place, like 23.839281.... or is it strictly the decimal end, 0.839281... ?
Edited by: kavon89 on Oct 9, 2007 10:49 PM

Answer 1

I gave what the links said a shot, and I need some help debugging:
Here is what worked:
public class Main {
    public static void main(String[] args) {
        solveit();
    public static double factorial(double n) {
        if      (n <  0)  throw new RuntimeException("Can't be negative stupid.");
        else if (n > 100) throw new RuntimeException("Number too big at the moment! :(");
        else if (n == 0)  return 1;
        else              return 1 / (n * factorial(n-1));
    public static void solveit() {
        double z = 2;
        System.out.println(factorial(z));
Here is what I tried to get BigDecimals in there:
public class Main {
    public static void main(String[] args) {
        solveit();
    public static BigDecimal factorial(BigDecimal n) {
        BigDecimal m = new BigDecimal("1");
        n = n.setScale(5);
        return m.divide((n.multiply(factorial(n.subtract(m)))));
    public static void solveit() {
        BigDecimal z = new BigDecimal("2");
        System.out.println(factorial(z)); //1 / 2! == 0.5
}and finally, my error:
Exception in thread "main" java.lang.StackOverflowError
        at java.lang.Character.digit(Character.java:4494)
        at java.lang.Long.parseLong(Long.java:401)
        at java.lang.Long.parseLong(Long.java:461)
        at java.math.BigDecimal.<init>(BigDecimal.java:452)
        at java.math.BigDecimal.<init>(BigDecimal.java:647)
        at Main.factorial(Main.java:23)
        at Main.factorial(Main.java:25)
        at Main.factorial(Main.java:25)
        // the line above this repeats MANY times, and the message ends with...
Java Result: 1
BUILD SUCCESSFUL (total time: 1 second)What is wrong? :s Help!
Edited by: kavon89 on Oct 9, 2007 11:43 PM