Binding HashMap to ComboBox

Question

Does anybody have an example of how to binding the keys of a HashMap to a ComboBox so that the changes in the HashMap are instantly reflected to 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 have it use a TreeMap<T> or some other child of SortedMap<T> as its data nucleus. I don't think that you'd want to use a HashMap since the model of a JComboBox needs to be ordered and a HashMap is not ordered.

The class should also extend the AbstractListModel<E> in order to gain the ListModel's functionality automatically saving you from having to maintain your own EventListenerList and giving you two of the bottom four methods in my list above for free, as well as some fireXXX(...) data change notification methods.

What you must do is create the necessary methods dictated by the MutableComboBoxModel<T> 's interface's API . This would only mean implementing 12 methods,

• 4 of 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 of ListModel<E> ,
  • void addListDataListener(ListDataListener listener) no need to write -- part of AbstractListModel
  • E getElementAt(int index)
  • int getSize()
  • void removeListDataListener(ListDataListener listener) no need to write -- part of AbstractListModel

This should be do-able, I should think.

Edit: on looking this over some more, I'm having an issue with insertElementAt(...) . Since I've advocated a SortedMap as the model's nucleus, you can't add an element arbitrarily into the a position in the Map since it is sorted by its "natural" order. This works best with using an ArrayList, Vector or other similar collection as the model's data nucleus.

Edit 2 : Much better to use a LinkedHashMap as per Omid's suggestion.