Longest Palindromic Substring

public class Solution {
    /**
     * @param s input string
     * @return the longest palindromic substring
     */
    public static String longestPalindrome(String s) {
        if (s == null || s.isEmpty()){
            return null;
        }
        int left = 0;
        int right = 0;
        int len = s.length();
        int longest = 0;
        for (int i = 0; i < len; i++){
            for (int j = i + 1; j <= len; j++){
                String cub = s.substring(i, j);
                if (isPalindroma(cub) && cub.length() > longest){
                    longest = cub.length();
                    left = i;
                    right = j;
                }
            }
        }
        String result = s.substring(left, right);
        return  result;

    }
    public static boolean isPalindroma(String s){
        if (s == null || s.isEmpty()){
            return false;
        }
        int len = s.length() - 1;
        for (int i = 0; i <= len; i++){
            if (s.charAt(i) != s.charAt(len - i)){
                return false;
            }
        }
        return true;
    }
}