@Override
    public boolean equals(Object obj) {

        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        UserManager other = (UserManager) obj;
        if (groups == null) {
            if (other.groups != null) {
                return false;
            }
        } else if (!groups.equals(other.groups)) {
            return false;
        }
        if (users == null) {
            if (other.users != null) {
                return false;
            }
        } else if (!users.equals(other.users)) {
            return false;
        }
        return true;
    }