SwingX provides a similar component called JXDatePicker which consists of two separate components (a JFormattedTextField and a JButton). Because we want to see a more homogenous design and we want to avoid tabbing through an additional component, we decided to build a complete new component which looks like a regular JComboBox.
In the demo you see two comboboxes, one is editable the other not. The used date format is DateFormat.LONG which can be easily changed. Take a look at the examples directory to learn more about the DateComboBox features.