Longest palindromic subsystem

gistfile1.txt

public class Solution {
    public String longestPalindrome(String ss) {
        if (ss == null) {
            return null;
        }
        
        if (ss.length() == 1) {
            return ss;
        }
        
        String longest = ss.substring(0, 1);
        for(int i=0; i<ss.length(); i++) {
            String centeredAtI = getSubstringFor(ss, i, i);
            if (centeredAtI.length() > longest.length()) {
                longest = centeredAtI;
            }
            
            String centeredAfter = getSubstringFor(ss, i, i+1);
            if (centeredAfter.length() > longest.length()) {
                longest = centeredAfter;
            }
        }
        return longest;
    }
    
    public String getSubstringFor(String s, int begin, int end) {
	    while (begin >= 0 && end < s.length() && s.charAt(begin) == s.charAt(end)) {
		    begin--;
		    end++;
	    }
	    return s.substring(begin + 1, end);
    }

}