Swing Hacks

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Chapter 1, Basic JComponents

#12 Add Translucence to Menus

HACK

No constructor is required because all UI classes have a no-arg constructor

automatically. All UI classes also need a static

createUI( ) method to create a

new instance of the class, as you can see in the example. In the

paint( )

method, instead of drawing on the graphics object passed in, the code cre-

ates a buffered image with the same dimensions as the component, and then

calls

super.paint( )

. This will draw the component onto the buffered image

instead of the screen. Once the painting is done, it can apply a transform and

then draw the image buffer onto the real

Graphics. In this case, the trans-

form is an alpha composite of

0.8. This means that instead of drawing the

buffer as is, it will draw the buffer partially transparent (80% solid, in this

case). This will draw the

bufferedimage into the real graphics with a translu-

cent effect. You can vary the strength of the translucency by modifying the

second parameter to the

AlphaComposite.getInstance( ) method (1 results in

a solid,

0 is totally transparent).

Add a Custom JMenu

If you stopped with just the custom menu items, the menus would seem a

bit translucent, but the rest of the window wouldn’t shine through. This is

because the menu items are inside of another component; in fact, they’re

inside of three! The

JMenu puts all of the menu items inside of a JPopupMenu,

which is placed