Longest Palindromic Substring Java

Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest
palindromic substring.

Have you been asked this question in an interview? 

   Idea: Nested loop:

    Outer loop: i start from back to front

    inner loop: j start from i to the end

Stated more formally below:

Define P[i][j] ← true iff

the substring Si … Sj is a palindrome,that means

Si = Sj and P[i][j] ← ( P[ i+1, j-1 ]

otherwise false.

public static String longestPalindrome(String s) {
if(s==null || s.length()==0) return "";
int len=s.length();
boolean[][] palin=new boolean[len][len];
String res="";
int maxLen=0;
for(int i=len-1;i>=0;i--){
for(int j=i;j<len;j++){
System.out.println(i+"->"+s.charAt(i)+" => "+j +"->"+s.charAt(j));
//System.out.println();
if(s.charAt(i)==s.charAt(j) && (j-i<=2 || palin[i+1][j-1])){
palin[i][j]=true;
if(maxLen<j-i+1){
maxLen=j-i+1;
res=s.substring(i,j+1);
System.out.println("res: "+res);
}
}
}
}
return res;
}