Java regex non-capturing group "?:"

1. see: http://stackoverflow.com/questions/3512471/non-capturing-group
2. usage: 

   (?:http|ftp)://([^/\r\n]+)(/[^\r\n]*)?

3. Match "http://stackoverflow.com/"
        Group 1: "stackoverflow.com"
        Group 2: "/"
   
   Match "http://stackoverflow.com/questions/tagged/regex"
        Group 1: "stackoverflow.com"
        Group 2: "/questions/tagged/regex"