Associate a HashMap with a ComboBox

Question

Does anyone have an example of how to bind HashMap keys to a ComboBox so that changes to the HashMap instantly reflect on the ComboBox?

Thanks!

EDIT:

Solution thanks to "Hovercraft Full Of Eels":

private Map<String, String> format = new LinkedHashMap<String,String>(); public class ToComboBoxModel<String> extends AbstractListModel<String> implements MutableComboBoxModel<String> { private String selectedItem; @Override public Object getSelectedItem() { return selectedItem; } @Override public void setSelectedItem(Object anItem) { // TODO Auto-generated method stub for (java.lang.String str : format.keySet()){ if (anItem.equals(str)) { selectedItem=(String) str; break; } } } @Override public String getElementAt(int index) { List<Entry<String,String>> randAccess = new ArrayList<Entry<String,String>>((Collection<? extends Entry<String, String>>) format.entrySet()); return randAccess.get(index).getKey(); } @Override public int getSize() { // TODO Auto-generated method stub return format.size(); } @Override public void removeElement(Object obj) { // TODO Auto-generated method stub } @Override public void removeElementAt(int index) { // TODO Auto-generated method stub } @Override public void addElement(String item) { } @Override public void insertElementAt(String item, int index) { // TODO Auto-generated method stub } } 

Answer 1

I would create a class that implements the MutableComboBoxModel<T> interface and uses it as a TreeMap<T> or some other SortedMap<T> child element as the data core. I don’t think you would like to use HashMap , since the JComboBox model has to be ordered and the HashMap is not ordered.

The class also needs to extend AbstractListModel<E> to get ListModel functionality, automatically eliminating the need to maintain your own EventListenerList and give you two of the bottom four methods in my list above for free, as well as some fireXXX(...) data notification methods fireXXX(...) .

What you need to do is create the necessary methods dictated by the MutableComboBoxModel<T> API . That would mean introducing 12 methods,

• 4 from MutableComboBoxModel<E> ,
  • void addElement(E item)
  • void insertElementAt(E item, int index)
  • void removeElement(E obj)
  • void removeElementAt(int index)
• 2 of ComboBoxModel<E> ,
  • E getSelectedItem()
  • void setSelectedItem(E item)
• and 4 from ListModel<E> ,
  • void addListDataListener(ListDataListener listener) no need to write - part of AbstractListModel
  • E getElementAt(int index)
  • int getSize()
  • void removeListDataListener(ListDataListener listener) does not need to be written - part of AbstractListModel

It should be helpful, I have to think.

Edit: When considering this more, I have a problem with insertElementAt(...) . Since I advocated SortedMap as the core of the model, you cannot add an element arbitrarily to the “on the map” position, since it is sorted in the “natural” order. This works best using an ArrayList, Vector, or other similar collection, such as the model data core.

Change 2 . It is much better to use LinkedHashMap as suggested by Omid.