Graphical User Interfaces - JavaTech: An Introduction to Scientific and Technical Computing with Java - page 221

cg = 0xFF;
cb = 0xFF;
}
fOutputPanel.setColor (cr,cg,cb);
} // valueChanged
} // class ListPanel
Note the use of the JScrollPane class, which provides scroll bars (vertical
and horizontal) for those components, such as JList and JTextArea , that
implement the Scrollable interface. The bars appear whenever the content
extends beyond the visible area of the component.
7.3.4 JSlider
Sliders allow the user to choose from a continuous range of values rather than from
discrete values as with a set of buttons or a list. In Figure 7.7, UiTestApplet
has selected SliderPanel as its control panel. The panel holds three instances
of JSlider . The user can move the sliders to select the values for the Red-
Green-Blue component values, each on a 0 to 255 scale. The combination of
these three color values becomes the background color of the OutputPanel .
Because of the continuous color changes possible, this is an applet that really
should be experienced live. To see the sliders in action, we encourage you either
to see the program on the Web Course site or to create the program from this
source code and run it on your own.
The constructor parameters set the orientation of the slider (horizontal or
vertical) and the upper and lower limit values. The last parameter sets the initial
value of the slider.
A slider sends instances of ChangeEvent to each of the entries added to its
ChangeListener list. The panel therefore implements the ChangeListener
interface and provides a stateChanged() method. The current value setting
on the slider is obtained easily with its getValue() method.
Figure 7.7 The JSlider component allows the user to select from a continuous
range of values. With the SliderPanel class displayed in UITestApplet , the three
sliders set the Red-Green-Blue component values from 0 to 255 each. The combined
RGB values determine the color of the background of the top area.