Valid Number

/*
*Validate if a given string is numeric.
*Some examples:
*v"0" => true
*" 0.1 " => true
*"abc" => false
*"1 a" => false
*v"2e10" => true
*Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.
*
*Update (2015-02-10):
*The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button  to reset your code definition.
*/

public class Solution {
    public boolean isNumber(String s) {
        if (s == null || s.trim().length() == 0) {
            return false;
        }
        s = s.trim();
        int i = 0;
        if (s.charAt(i) == '+' || s.charAt(i) == '-') {
            i++;
        }
        boolean hasE = false;
        boolean hasDot = false;
        boolean hasNum = false;
        for (; i < s.length(); i++) {
            char c = s.charAt(i);
            if (c == '.') {
                if (hasDot || hasE) {
                    return false;
                }
                hasDot = true;
            } else if(c == 'e' || c == 'E') {
                if (hasE || !hasNum || i == s.length() - 1) {
                    return false;
                }
                hasE = true;
            } else if(c == '+' || c == '-') {
                if (i - 1 >= 0 && (s.charAt(i - 1) == 'e' || s.charAt(i - 1) == 'E') &&  i != s.length() - 1) {
                    continue;
                } 
                return false;
            } else if(Character.isDigit(s.charAt(i))) {
                hasNum = true;
            } else {
                return false;
            }
        }
        return hasNum;
    }
}