What is wrong with the following method for calculating factorials?

/** * Calculates the factorial of a non-negative integer, that is, the product of * all integers between 1 and the given integer, inclusive. * The worstTime(n) is O(n), where n is the given integer.

*

* @param n the non-negative integer whose factorial is calculated. *

* @return the factorial of n. *

* @throws IllegalArgumentException if n is less than 0. *

*/ public static long factorial (int n) {

if (n < 0) throw new IllegalArgumentException( );

if (n <= 1) return 1;

return fact (n+1) / (n+1); } // fact