How to fetch users from group?

private String[] getUsersFromGroup(String groupName){

String[] userLogins = null;

Set retAttrs = new HashSet();

RoleManager roleManager = null;

Role role = null;

try {

roleManager = Platfomr.getService(RoleManager.class);

role = roleManager.getDetails(RoleManagerConstants.ROLE_NAME, groupName, retAttrs);

String roleKey = role.getEntityId();

List <User> listOfUsers = roleManager.getRoleMembers(roleKey, true);

int size = listOfUsers.size();

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

User user =  listOfUsers.get(i);

String userLogin = user.getLogin();

userLogins = userLogin;

}

}catch(Exception e) {

e.printStackTrace();

}

return userLogins;

}