Swing Hacks

Building a Drop-Down Menu Button #10

Chapter 1, Basic JComponents

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HACK

H A C K

#10

Building a Drop-Down Menu Button

Hack #10

This hack shows how to build a color chooser as a proper drop-down

component. It will behave like

JComboBox but without the extension

headaches of Sun’s version of the class.

Most custom Swing components are created with simple subclasses of the

standard base classes in

javax.swing

. This works fine most of the time, but

every now and then you need to build something where there is no easy

standard component to start with. Even worse, sometimes the obvious

choice for your starting point is a component so convoluted that you can’t

figure out where to start. Still, you’d rather not reimplement the wheel. No,

I’m not talking about

JTree or JTable—I’m referring to the JComboBox. It

seems like such a simple component, but the implementation is fiendishly

complex.

Most large applications use components that feel like the

JComboBox, but do

something entirely different, like select a color or show a history list. A quick

search through the

JComboBox API doesn’t turn up any obvious extension

points. You could customize it with some cell renderers, but if you need a

component that doesn’t show a list of data, you are pretty much out of luck.

The source to

JComboBox is not very helpful either. The work is spread out

over several UI classes in the various Look and Feel (L&F) packages. If you

did ...