Learning Java
Chapter 14: Using Swing Components
All we've really done here is added a JScrollBar and a
JSlider to our main window. If the user adjusts either of
these components, the current value of the component is displayed in a
JLabel at the bottom of the window.
The JScrollBar and JSlider are both created by
specifying an orientation, either HORIZONTAL or
VERTICAL. You can also specify the minimum and maximum values
for the components, as well as the initial value. The
JScrollBar supports one additional parameter, the
extent. The extent simply refers to what range of values is
represented by the slider within the scroll bar. For example, in a
scrollbar that runs from 0 to 255, an extent of 128 means that the slider
will be half the width of the scrollable area of the scrollbar.
JSlider supports the idea of tick marks, which are lines drawn
at certain values along the slider's length. Major tick marks are
slightly larger than minor tick marks. To draw tick marks, just
specify an interval for major and minor tick marks, and then paint the tick marks:
slider.setMajorTickSpacing(48);
slider.setMinorTickSpacing(16);
slider.setPaintTicks(true);
JSlider also supports labeling the ticks with text strings,
using the setLabel-Table( ) method.
Responding to events from the two components is straightforward. The
JScrollBar sends out AdjustmentEvents every time
something happens; the JSlider fires off
ChangeEvents when its value changes. In our simple example, we
display the new value of the changed component in the JLabel
at the bottom of the window.
Dialogs
A dialog is another standard feature of user interfaces. Dialogs are
frequently used to present information to the user ("Your fruit salad is
ready.") or to ask a question ("Shall I bring the car around?"). Dialogs
are used so commonly in GUI applications that Swing includes a handy set of
pre-built dialogs. These are accessible from static methods in the
JOptionPane class. Many variations are possible;
JOptionPane groups them into four basic types:
- message dialog
- Displays a message to the user, usually accompanied
by an OK button.
- confirmation dialog
- Ask a question and displays answer buttons, usually
Yes, No, and Cancel.
- input dialog
- Asks the user to type in a string.
- option dialogs
- The most general type--you pass it your own
components, which are displayed in the dialog.
A confirmation dialog is shown in Figure 14-10.
Figure 14-10. Using a confirmation dialog
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