validnumber.java

public class valid_number {
    public boolean isNumber(String S) {
        boolean num = false, exp = false, sign = false, dec = false;
        for (int i = 0; i < S.length(); i++) {
            char c = S.charAt(i);
            if (c >= '0' && c <= '9') num = true;
            else if (c == 'e' || c == 'E')
                if (exp || !num) return false;
                else {
                    exp = true;
                    sign = false;
                    num = false;
                    dec = false;
                }
            else if (c == '+' || c == '-')
                if (sign || num || dec) return false;
                else sign = true;
            else if (c == '.')
                if (dec || exp) return false;
                else dec = true;
            else return false;
        }
        return num;
    }
}