public class Sum {
// Java program to find and print the sum of the series on the next line below.
//    1 + (1/2) - (1/3) + (1/4) - (1/5) ...
    /**
     * Method prints the sum of the given series using recursive computation
     * and calling itself at the return statement. A special case is
     * considered when N == 1, and it should throw an exception for N < 1.
     *
     * @param n - is the number of terms. Higher values for this variable
     *          correspond to increased accuracy for the sum of this series.
     * @return calls "fancySumRecursive" to in fact be recursive.
     */
    public static double fancySumRecursive(long n) {
        if (n < 1) {
            throw new IllegalArgumentException("Number of terms must"
                    + "be greater than 0");
        } else if (n == 1) {
            return 1.0;
        }
        return 1.0 / n + fancySumRecursive(n - 1);
    }
    // Driver code
    public static void main(String[] args) {
        int n = 100;
        // I set the print to 100 places after the decimal to observe where
        // the precision of this method can compute the sum.
        System.out.printf("%.100f", fancySumRecursive(n-1));
    }
}
// This recursive method computes the sum to be the value below.
// 5.17737751763962100000000000000000000000000000000000000000000000000000
// My old non-recursive version of this program gave me the value below.
// 5.18737751763962100000000000000000000000000000000000000000000000000000