Longest Substring Without Repeating Characters

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        if(s==null||s.length()<1) return 0;
        int w =0, r = 0, len = 1;
        HashSet<Character> hs = new HashSet<Character>();
        while(r<s.length()){
            if(hs.contains(s.charAt(r))){
                len = Math.max(len, r-w);
                while(s.charAt(w)!=s.charAt(r)){
                    hs.remove(s.charAt(w)); // !!!!
                    w++;
                }
                w++; ///!!!
            }else{
                hs.add(s.charAt(r));
            }  
            r++;
        }
        return Math.max(len,r-w);
    }
}