GUI COMPONENTS - Introduction to Java Programming - page 654

By default, the selection mode of the list is multiple-interval, which allows the user to
select multiple items from different blocks in the list. When the user selects countries in the
list, the valueChanged handler (lines 58-72) is executed, which gets the indices of the
selected items and sets their corresponding image icons in the label to display the flags.

17.13 How do you create a list with an array of strings?
17.14 How do you set the visible row count in a list?
17.15 What selection modes are available for a list? How do you set a selection mode?
17.16 How do you set the foreground and background color of a list? How do you set the
foreground and background color of the selected items?

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Check

Point

17.6 Scroll Bars
JScrollBar is a component that enables the user to select from a range of values.

Key
Point

Figure 17.10 shows a scroll bar. Normally, the user changes the value of the scroll bar by mak-
ing a gesture with the mouse. For example, the user can drag the scroll bar's bubble up and
down, or click in the scroll bar's unit-increment or block-increment areas. Keyboard gestures
can also be mapped to the scroll bar. By convention, the Page Up and Page Down keys are
equivalent to clicking in the scroll bar's block-increment and block-decrement areas.

Minimum value Maximum value

Block decrement Block increment

Bubble

Unit decrement Unit increment

F IGURE 17.10

A scroll bar represents a range of values graphically.

Note
The width of the scroll bar's track corresponds to maximum + visibleAmount .
When a scroll bar is set to its maximum value, the left side of the bubble is at maximum ,
and the right side is at maximum + visibleAmount .

JScrollBar has the following properties, as shown in Figure 17.11.
When the user changes the value of the scroll bar, the scroll bar fires an AdjustmentEvent .
A listener class for this event must implement the adjustmentValueChanged handler in the
java.awt.event.AdjustmentListener interface.
Listing 17.6 gives a program that uses horizontal and vertical scroll bars to control a mes-
sage displayed on a panel. The horizontal scroll bar is used to move the message to the left
and the right, and the vertical scroll bar to move it up and down. A sample run of the program
is shown in Figure 17.12.
Here are the major steps in the program:

1. Create the user interface.
Create a MessagePanel object and place it in the center of the frame. Create a vertical
scroll bar and place it in the east of the frame. Create a horizontal scroll bar and place it
in the south of the frame.