public void removeUser(String username_) {
   Enumeration e = _users.elements();
   while (e.hasMoreElements()) {
     User u = (User) e.nextElement();
     if (u.account.equals(username_)) {
       _users.remove(u);
       break;
     }
   }
 }
 public Object getValueAt(int row_, int column_) {
   // later....
   User user = (User) _users.elementAt(row_);
   switch (column_) {
     case 0:
       return user.account;
     case 1:
       return user.fullname;
     default:
       return "Invalid";
   }
 }
 public int getRowCount() {
   return _users.size();
 }
 public void addUser(User user_) {
   _users.add(user_);
 }