BigFactorial.java

import java.util.Scanner;
import java.math.BigInteger;

public class BigFactorial {

    /** Program:    BigFactorial.java
    *   Purpose:    Find n! up to 10000! using Big Integers
    *   Creator:    Chris Clarke
    *   Created:    16.07.2012
    */

    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.print( "Enter a number (max 10000): ");
        int n = keyboard.nextInt();
        BigInteger bigInt = new BigInteger (""+n);
        System.out.println( "The factorial of "+n+" = "+n+"! = "+factorial( bigInt));
    }

    public static BigInteger factorial( BigInteger b) {
        return b.equals(BigInteger.ONE)?
         BigInteger.ONE:
         b.multiply( factorial( b.subtract( BigInteger.ONE)));
    }
}