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Learning Java : Chapter 14: Using Swing Components

Buy this book Title: Learning Java ISBN: 1565927184 Order No 7184 US Price: $ 34.95 Publication Date: May 2000 Pages: 722 © O'Reilly & Associates, Inc. Author's Top Ten Tips and Tricks

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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