Swing Hacks

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Chapter 2, Lists and Combos

#19 Turn Methods into List Renderers

HACK

setting a flag so that the cell renderer applies only the colorized foreground

and background colors to that cell.

H A C K

#19

Turn Methods into List Renderers Hack #19

By using a little bit of reflection, you can make a generic ListCellRenderer

that can render data using any method at runtime.

JLists, like JTable and JTree, use a decorator pattern to customize how they

look. This system of cell renderers works well, but it can require you to

build a unique renderer class for each type of object you want to put into

your lists. Often, all you really want to do is call a particular method on the

objects in your list, but writing a complete class to just call one method is a

lot of work for such a small task. This hack shows you how to use reflection

to create a generic cell renderer that can be reused on any object without

subclassing.

Building a Generic Renderer

The default JList cell renderer will just call toString( ) on the objects in the

list and draw the resulting string to the screen. This is fine for simple uses

where you really are just looking at a list of strings or objects with appropri-

ate

toString( ) methods. More complicated applications—and they all

become more complicated eventually—require more complicated objects,

and those objects might not have a convenient or useful

toString( ) method.

Eventually, you have to ...