Learning Java

Lists and Combo Boxes

JLists and JComboBox es 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 the user to choose a single selection or to allow multiple choices. Usually, only a small group of choices are 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. He or 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.

A combo box is a cross-breed between a text field and a list. It displays a single line of text (possibly with an image) and a downward pointing arrow at 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 every other component 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 may 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 ...