125. Valid Palindrome

1     public boolean isPalindrome(String s) {
2         if(s == null || s.length() == 0) {
3             return true;
4         } 
5         s = s.toLowerCase();
6         s = s.replaceAll("[^a-z0-9]","");
7         StringBuilder sb = new StringBuilder(s);
8         return s.equals(sb.reverse().toString());
9     }