Find factorial of large numbers in Java

You might want to reconsider calculating this huge value. Wolfram Alpha's Approximation suggests it will most certainly not fit in your main memory to be displayed.

public static void main(String[] args) {
    BigInteger fact = BigInteger.valueOf(1);
    for (int i = 1; i <= 8785856; i++)
        fact = fact.multiply(BigInteger.valueOf(i));
    System.out.println(fact);
}

This code should work fine :-

public class BigMath {
    public static String factorial(int n) {
        return factorial(n, 300);
    }

    private static String factorial(int n, int maxSize) {
        int res[] = new int[maxSize];
        res[0] = 1; // Initialize result
        int res_size = 1;

        // Apply simple factorial formula n! = 1 * 2 * 3 * 4... * n
        for (int x = 2; x <= n; x++) {
            res_size = multiply(x, res, res_size);
        }

        StringBuffer buff = new StringBuffer();
        for (int i = res_size - 1; i >= 0; i--) {
            buff.append(res[i]);
        }

        return buff.toString();
    }

    /**
     * This function multiplies x with the number represented by res[]. res_size
     * is size of res[] or number of digits in the number represented by res[].
     * This function uses simple school mathematics for multiplication.
     * 
     * This function may value of res_size and returns the new value of res_size.
     */
    private static int multiply(int x, int res[], int res_size) {
        int carry = 0; // Initialize carry.

        // One by one multiply n with individual digits of res[].
        for (int i = 0; i < res_size; i++) {
            int prod = res[i] * x + carry;
            res[i] = prod % 10; // Store last digit of 'prod' in res[]
            carry = prod / 10;  // Put rest in carry
        }

        // Put carry in res and increase result size.
        while (carry != 0) {
            res[res_size] = carry % 10;
            carry = carry / 10;
            res_size++;
        }

        return res_size;
    }

    /** Driver method. */
    public static void main(String[] args) {
        int n = 100;

        System.out.printf("Factorial %d = %s%n", n, factorial(n));
    }
}