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.

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   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;    }