Using for-each loop this is optimize way...

for(userdata obj : dataList){

   System.out.println("User ID :: " + obj.userid);
   System.out.println("Group ID :: " + obj.groupid);
   .
   .
   .

}

Using for loop

for(int i =0;i<datalist.size();i++){

       userdate obj=datalist.get(i);
       System.out.println("User ID :: " + obj.userid);
       System.out.println("Group ID :: " + obj.groupid);
       .
       .
       .

    }