Bounded Range Components - The Definitive Guide to Java Swing - page 413

DefaultBoundedRangeModel has two constructors:
public DefaultBoundedRangeModel()
public DefaultBoundedRangeModel(int value, int extent, int minimum, int maximum)
The no-argument version sets up the minimum , value , and extent properties of the model
to have a setting of 0. The remaining maximum property gets a setting of 100.
The second constructor version takes four integer parameters, explicitly setting four proper-
ties. For both constructors, the initial value of the valuelsAdjusting property is false because
the value of the model isn't yet changing beyond the initial value.
■ Note Unless you're sharing a model across multiple components, it generally isn't necessary to create a
BoundedRangeModel . Even if you're sharing a model across multiple components, you can create just the
first component and get its BoundedRangeModel model to share.
As with practically all of the classes that manage their own listener lists, you can ask
DefaultBoundedRangeModel for the listeners assigned to it. Here, you ask the model for its
ChangeListener list with getListeners(ChangeListener.class) . This returns an array of
EventListener objects.
JScrollBar Class
The simplest of the bounded range components is the JScrollBar . The JScrollBar component
is used within the JScrollPane container, described in Chapter 11, to control the scrollable
region. You can also use this component within your own containers, although with the flexibility
of JScrollPane this typically isn't necessary. The one point to remember about JScrollBar ,
however, is that it isn't used for the entry of a value, but solely for the scrolling of a region of
screen real estate. For the entry of a value, you use the JSlider component discussed in the
next section.
■ Note The JScrollBar within a JScrollPane is actually a specialized subclass of JScrollBar that
properly deals with scrollable components that implement the Scrollable interface. Although you can
change the scrollbars of a JScrollPane , it's usually unnecessary—and more work than you might think.
As Figure 12-2 shows, the horizontal JScrollBar is composed of several parts. Starting
from the middle and working outward, you find the scrollbar's thumb —also called a knob or
slider . The width of the thumb is the extent property from the BoundedRangeModel . The current
value of the scrollbar is at the left edge of the thumb. To the immediate left and right of the
thumb are the block paging areas. Clicking to the left of the thumb will decrement the scrollbar's
value, while clicking to the right increments it. The increased or decreased amount of the
scrollbar's value is the scrollbar's blockIncrement property.