The factorial function using recursion

factorial_recursive.java

    private static long factorialTopDownRecursion(long n) {
        // base case
        if (n <= 1)
            return 1;

        return n * factorialTopDownRecursion(n-1);
    }

    private static long factorialBottomUpRecursion(long n) {
        return _factorialBottomUpRecursion(1, n);
    }

    private static long _factorialBottomUpRecursion(long n, long upperBound) {
        // base case
        if (n > upperBound)
            return 1;

        return n * _factorialBottomUpRecursion(n+1, upperBound);
    }