private String generatePrefix(Object obj){
        
        String prefix ="";
        
        if (obj instanceof User){
            User u = (User) obj;
            if(u.isOnline())
                return "USER_AAA_";
            else
                return "USER_BBB_";
        }
        else if( obj instanceof Arena){
            return "AAAAA_";
        }
        else
            return "";
        
        
    }