Factorial: OO x OO (FP inspired)

Factorial Class

public class Factorial {

	public static long declarativeFactorial(int n){
		assert n > 0 : "Argument must be greaten than 0";
		if (n == 1)
			return 1;
		else 
			return n * declarativeFactorial(n-1);
	}
	
	public static long imperativeFactorial(int n){
		assert n > 0 : "Argument must be greaten than 0";
		
		long result = 1;
		
		for (int i = 2; i<= n; i++) {
			result *= i;
		}
		return result;
	}
}