leetcode-Longest Substring Without Repeating Characters

public class Solution {     public int lengthOfLongestSubstring(String s) {        Map<String, Integer> map = new HashMap<String, Integer>();        int max = 0;        int length=0;        int start = 0;        for(int i=0;i<s.length();i++){            if(!map.containsKey(s.substring(i,i+1)) || map.get(s.substring(i, i+1)) < start){                length++;            } else {                int tmp=i-map.get(s.substring(i,i+1));                length = tmp > length?length:tmp;                start = tmp > length?start:map.get(s.substring(i,i+1));            }            map.put(s.substring(i,i+1), i);            if(length>max) {                max=length;            }        }        return max;    }     }