Preferred way of getting the selected item of a JComboBox

If you have only put (non-null) String references in the JComboBox, then either way is fine.

However, the first solution would also allow for future modifications in which you insert Integers, Doubless, LinkedLists etc. as items in the combo box.

To be robust against null values (still without casting) you may consider a third option:

String x = String.valueOf(JComboBox.getSelectedItem());