Swing Hacks

Add a Watermark to a Text Component #5

Chapter 1, Basic JComponents

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HACK

H A C K

#5

Add a Watermark to a Text Component

Hack #5

This hack will show how to create a custom image background for the

JTextField, a complex Swing component that does not already support

backgrounds or icons by default.

One of Swing’s most underused features is the ability to partially override

drawing code. Most programs enhance widgets by using renderers or com-

pletely overriding the paint code. By only partially overriding the drawing,

however, you can create some very interesting effects that blend both new

and existing drawing commands.

Some components, like

JList and JTable, use renderers to customize their

look. To put a background in a

JTextField, however, requires more. The

plan is to subclass

JTextField, prepare the resources for drawing a back-

ground (loading the image, etc.), and then draw a new background while

preserving the normal

JTextField drawing code for the text and cursor.

The actual drawing will be done with a

TexturePaint. Java2D allows you to

fill any area with instances of the

Paint interface. Typically you use a color,

which is an implementation of

Paint, but it is possible to use something else,

such as a texture or gradient. This class will use a

TexturePaint to tile an

image across the component’s background.

The first step is to create a

JTextField subclass (shown in Example 1-10).

Example 1-10 creates ...