Sum Of String Values

/**
 *
 * @author Aamir khan
 */
public class SumOfStrings {

    /**
     * @author Aamir khan
     */
    public static void main(String[] args) {

        //direct sum
        System.out.println(
                "123".chars().map(i -> Character.digit(i, 10)).sum()
        );

        //filter numeric values
        System.out.println(
                "123four".chars().filter(SumOfStrings::isNum).map(i -> Character.digit(i, 10)).sum()
        );

        //old school solution
        int sum = 0;
        for (char c : "four321".toCharArray()) {
//            if (c < 48 || c > 58) continue;
            if (!isNum(c)) continue;
            sum += Character.digit(c, 10);
        }
        System.out.println(sum);
    }

    private static boolean isNum(int c){
        return Character.isDigit(c);
    }
}