public boolean isNumber(String s)

	{

        s = s.trim();

        if (s.length() == 0) return false;

        boolean hasE = false;

        boolean hasDot = false;

        boolean hasNumber = false;

        for (int i = 0; i < s.length(); i++)

        {

            // e cannot be the first character

            if (i == 0 && s.charAt(i) == 'e') return false;

            if (s.charAt(i) == 'e') {

                // e cannot be replicated nor placed before number

                if (hasE == true || hasNumber == false) {

                    return false;

                } else {

                	hasE = true;

                }

            } 

            if (s.charAt(i) == '.') {

                // '.' cannot be replicated nor placed after 'e'

            	if (hasDot == true || hasE == true) {

                	return false;

                } else {

                	hasDot = true;

                }

            }

            // the sign can be placed at the beginning or after 'e'

            if (i != 0 && s.charAt(i - 1) != 'e' && (s.charAt(i) == '+' || s.charAt(i) == '-')) return false;

            // no other chacraters except '+', '-', '.', and 'e'

            if ((s.charAt(i) > '9' || s.charAt(i) < '0') && s.charAt(i) != '+' && s.charAt(i) != '-' && s.charAt(i) != '.' && s.charAt(i) != 'e')

            return false;  

            // check whether numbers are included.

            if (s.charAt(i) <= '9' && s.charAt(i) >= '0')

            {

                hasNumber = true;

            }

        }

        // '+', '-', and 'e' cannot be the last character

        if (s.charAt(s.length() - 1) == '-' || s.charAt(s.length() - 1) == '+' || s.charAt(s.length() - 1) == 'e') return false;

        return hasNumber;

    }

}