Whether it is for combobox or something else, it is irrelevant. What you need is a way to read the info from the database and put them into a list (Vector).
Then you can use the data into the Vector and put wherever you want (JComboBox)
Search this forum, there are examples on how to connect to database using java.
You will need to create the connection, then use the query and the connection to create a statement and then run it to get the results.
Search this forum for examples