JavaAlgorithms/Maths/Factorial.java

package Maths;

public class Factorial {

    /* Driver Code */
    public static void main(String[] args) {
        assert factorial(0) == 1;
        assert factorial(1) == 1;
        assert factorial(5) == 120;
        assert factorial(10) == 3628800;
    }

    /**
     * Calculate factorial N using iteration
     *
     * @param n the number
     * @return the factorial of {@code n}
     */
    public static long factorial(int n) {
        if (n < 0) {
            throw new IllegalArgumentException("number is negative");
        }
        long factorial = 1;
        for (int i = 1; i <= n; factorial *= i, ++i) ;
        return factorial;
    }
}