leetcode solution 125 valid palindromw

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

For example,
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

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class  {
    public boolean isPalindrome(String s) {
        int i = 0;
        int j = s.length()-1;
        while(i<j) {
            if(!Character.isLetterOrDigit(s.charAt(i))) i++;
            else if(!Character.isLetterOrDigit(s.charAt(j))) j--;
            else if(Character.toUpperCase(s.charAt(i))!=Character.toUpperCase(s.charAt(j)))
                return false;
            else{
                i++;
                j--;
            }
        }
        return true;
    }
}

• please pay attention to the code inside while loop, where if-else clause should be used to avoid OutOfIndex error.