Swing Hacks

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Chapter 1, Basic JComponents

#6 Watermark Your Scroll Panes

HACK

H A C K

#6

Watermark Your Scroll Panes

Hack #6

This hack creates a text area with a tiled background image that is fixed,

even when the text area scrolls, and also a fixed foreground image that

appears above the text, much like the station badges now affixed to the

lower-righthand corner of most TV broadcasts.

The Swing framework was designed to let developers override portions of

every component, both the visual appearance (the view) and the behavior

(the model and controller). This design gives developers great flexibility.

One of my favorites is the

JScrollPane. Its nested composite design allows

developers to create some stunning effects.

Once again, the idea is to override the drawing code of a standard compo-

nent to create the visual effects

[Hack #5]. The difference here is that you must

deal with a composite object, the

JScrollPane. A JScrollPane is not a single

Swing component—it’s actually a wrapper around two scrollbars and the

component that does the real scrolling is a

JViewport. This viewport is the

actual target component; you will subclass it to draw both above and below

the

View component (as seen in Example 1-12). The View is the Swing wid-

get being scrolled; in this case, it is a

JTextArea.

The

ScrollPaneWatermark class inherits from JViewport, adding two meth-

ods:

setBackgroundTexture( ) and setForegroundBadge( ). Each ...