按字母顺序对ComboBox中的项目进行排序？

Question

我想开始说这个项目我不能使用任何类型的List。我在线搜索过，所有建议通常都说是使用ArrayList。所以我需要帮助找到另一种方法来做到这一点。确定..

我有一个GUI，它有一个ComboBox，显示从文件中读取的城市列表。我有那个部分就好了。但是城市需要按字母顺序排列。这发生在这两个类

中

ReadButton Listener类：

class ReadListener implements ActionListener {

public void actionPerformed(ActionEvent arg0)
{
  Scanner cityData = null;
  try
  {
    cityData = new Scanner(new File(CityGUI.this.inputFile.getText()));
  }
  catch (FileNotFoundException e)
  {
    CityGUI.this.inputMessage.setForeground(Color.RED);
    CityGUI.this.inputMessage.setText("File not found");
  }
  cityData.nextLine();

  //reads the file until there is no more data to be read
  while (cityData.hasNextLine()) {
        Scanner lineScanner = new Scanner(cityData.nextLine());
        lineScanner.useDelimiter(",");

        int zip = lineScanner.nextInt();
        String cityName = lineScanner.next();
        String state = lineScanner.next();
        double lat = lineScanner.nextDouble();
        double lon = lineScanner.nextDouble();
        int time = lineScanner.nextInt();
        String restOfLine = lineScanner.nextLine();
        boolean dayLight;
        if (restOfLine.charAt(1) == '1') {
          dayLight = true;
        } else {
          dayLight = false;
        }
        City newCity = new City(zip, cityName, state, lat, lon, time, dayLight);
        CityGUI.this.cityList.addCity(newCity);
      }

  CityGUI.this.inputMessage.setForeground(Color.BLUE);
  CityGUI.this.inputMessage.setText("The cities have been read");

  String[] cityNames = CityGUI.this.cityList.getCityNames();

  //add the cities to the list displayed in the combo box
  for (int i = 0; i < cityNames.length; i++) {
    CityGUI.this.cityCombo.addItem(cityNames[i]);
  }
}
}

和我的CityGroup课程：

public class CityGroup
{
private final int numCities = 30;
private City[] cityArray = new City[numCities];
private int count = 0;

//adds cities read from the file to an array
public void addCity(City newCity)
{
  cityArray[count] = newCity;
    count++;
}

//read the names from the cityArray and returns them when called
public String[] getCityNames()
{
String[] names = new String[numCities];

for (int i = 0; i < count; i++) {
  names[i] = cityArray[i].getCityName();
}
return names;
}


public City getCity(String cityName)
{
for (int i = 0; i < numCities; i++) {
  if (cityArray[i].getCityName().equals(cityName)) {
    return cityArray[i];
  }
}
return null;
}
}

.compareTo也没用。