Learning Java, 4th Edition

Lists and Combo Boxes

JLists and JComboBoxes are a step up on the evolutionary chain from JButtons and JLabels. Lists let the user choose from a group of alternatives. They can be configured to force a single selection or allow multiple choices. Usually, only a small group of choices is displayed at a time; a scrollbar lets the user move to the choices that aren’t visible. The user can select an item by clicking on it. She can expand the selection to a range of items by holding down Shift and clicking on another item. To make discontinuous selections, the user can hold down the Control key instead of the Shift key (on a Mac, this is the Command key).

A combo box is a crossbreed between a text field and a list. It displays a single line of text (possibly with an image) and a downward-pointing arrow on one side. If you click on the arrow, the combo box opens up and displays a list of choices. You can select a single choice by clicking on it. After a selection is made, the combo box closes up; the list disappears, and the new selection is shown in the text field.

Like other components in Swing, lists and combo boxes have data models that are distinct from visual components. The list also has a selection model that controls how selections can be made on the list data.

Lists and combo boxes are similar because they have similar data models. Each is simply an array of acceptable choices. This similarity is reflected in Swing, of course: the type of a JComboBox’s data model is a subclass ...