Java Swing, 2nd Edition

The JScrollBar Class

JScrollBar is the Swing implementation of a scrollbar. The JScrollBar class is shown in various L&Fs in Figure 6-3.

Figure 6-3. Scrollbars in several L&Fs

To program with a scrollbar, it is important to understand its anatomy. Scrollbars are composed of a rectangular tab, called a slider or thumb , located between two arrow buttons. The arrow buttons on either end increment or decrement the slider’s position by an adjustable number of units, generally one. In addition, clicking in the area between the thumb and the end buttons (often called the paging area) moves the slider one block, or 10 units by default. The user can modify the value of the scrollbar in one of three ways: by dragging the thumb in either direction, by pushing on either of the arrow buttons, or by clicking in the paging area.

Scrollbars can have one of two orientations: horizontal or vertical. Figure 6-4 provides an illustration of a horizontal scrollbar. JScrollBar uses the bounded-range model to represent the scrollbar’s data. The assignment of each bounded-range property is also shown in Figure 6-5. The minimum and maximum of the scrollbar fall on the interior edges of the arrow buttons. The scrollbar’s value is defined as the left (or top) edge of the slider. Finally, the extent of the scrollbar defines the width of the thumb in relation to the total range. (The older Adjustable interface ...