#N709. To Lower Case
problem link

#solution

class Solution {
    public String toLowerCase(String s) {
        char[] res=s.toCharArray();
        
        for(int i=0; i<res.length; i++){
            if(res[i]>='A'&&res[i]<='Z')
                res[i]=(char)(res[i]+32);
        }
        
        return String.valueOf(res);
    }
}

or another option, using the String method toLowerCase(), just write return s.toLowerCase(); .