Length of Last Word

Given a string s consists of upper/lower-case alphabets and empty space characters ' ', return the length of last word in the string.

If the last word does not exist, return 0.

Note: A word is defined as a character sequence consists of non-space characters only.

For example, 
Given s = "Hello World",
return 5.

public class Solution {    public int lengthOfLastWord(String s) {        int length=s.length();        int res=0;        if(length==0) return 0;        //for(int i=length-1;i>=0,i--)        int i=length-1;        while(i>=0&&s.charAt(i)==' ')           i--;           while(i>=0&&s.charAt(i)!=' ')               {                  i--;                 res++;               }          return res;     }}