Question: Is there a way to synchronize the entry values of a hashmap with a JComboBox. This means that as i add put more items to the hash map, the JComboBox is automatically aware that new items can be selected.

Answer: 
You could create your own combobox model by extending `AbstractListModel<E>`, implementing `ComboBoxModel<E>`, `ListModel<E>`, `MutableComboBoxModel<E>`, and using a `TreeMap<T, E>` as the nucleus of the model class (TreeMap instead of HashMap since the combobox model's data must be maintained in a certain order). Just be sure to fire the proper data change methods whenever data is added or removed from your HashMap.
extends HashMap to implement Observable interface just put Observor update function in 
add method of HashMap and listen for update in your jComboBox