Swing Hacks

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Chapter 1

C H A P T E R O N E

Basic JComponents

Hacks 1–12

Swing is a powerful toolkit, filled to the brim with complicated compo-

nents, extension APIs, and large Model-View-Controller (MVC) systems. It

can be quite daunting. The current edition of O’Reilly’s Java Swing book

now stretches over 1,200 pages! Swing now extends from the simplest

JButton to the full Look and Feel API. I am still amazed at the power and

flexibility of Swing, and quite aware of its complexity. Some of the more

esoteric parts can take years to master. However, you don’t need to go

straight into the

JTree or Look and Feel APIs just to do something cool.

There are still a lot of fun things waiting in the standard components we

don’t always think about.

This chapter covers some of the basic components that every Swing devel-

oper uses: buttons, labels, menus, and the occasional scroll pane. From this

base you will learn how to create image buttons, put watermarks into your

text areas, and even build a new component or two. These are the compo-

nents that seem boring, but with a little imagination, they can do a whole

lot, and the techniques here lay the foundation for even more exciting hacks

later in the book.

H A C K

#1

Create Image-Themed Components Hack #1

This hack shows how to use Swing’s built-in image support to create a

completely custom image-based user interface.

Most Swing applications get their look from a Look and Feel (L&F)—either

a standard one provided by the VM or a custom one. L&Fs are a whole lot

of work to build and still aren’t completely custom. You can redefine a but-

ton to look like red stoplights, but then all buttons throughout your applica-

tion will look like red stoplights. Sometimes all you really want is a look

built entirely out of images, much like image-based web navigation.

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Chapter 1, Basic JComponents

#1 Create Image-Themed Components

HACK

To give you an idea of where this hack is going, Figure 1-1 shows our target:

a frame with a panel containing a label, a button, and a checkbox. The

panel, label, and button will be completely drawn with images, using none

of the standard L&F. The checkbox will be a standard checkbox, but it

should be transparent to fit in with the image background.

The first step toward image nirvana is the background. Because this type of

component is quite reusable, I built a subclass of

JPanel called ImagePanel,

shown in Example 1-1.

The constructor takes the image to draw and saves it for later use in the

img

variable. Then it calls setSize( ) and setPreferredSize( ) with the size of the

image. This ensures that the panel will be the size of the image exactly. I had

Figure 1-1. A component rendered with images

Example 1-1. A Custom subclass of JPanel

public class ImagePanel extends JPanel {

private Image img;

public ImagePanel(Image img) {

this.img = img;

Dimension size = new Dimension(img.getWidth(null),

img.getHeight(null));

setSize(size);

setPreferredSize(size);

setMinimumSize(size);

setMaximumSize(size);

setLayout(null);

}

}

Create Image-Themed Components #1

Chapter 1, Basic JComponents

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HACK

to set the preferred, maximum, and minimum sizes as well—this is because

the panel’s parent and children may not be using absolute layouts.

Absolute layout means that there is no layout manager to

position the components appropriately (which can be set by

calling

setLayout(null)).

In this case, the explicit size and position will be used (via

setSize( )

and

setLocation( )

). When a layout manager is set, the preferred, minimum, and

maximum sizes may be used. To cover all of the bases, simply set all four

values to the image size.

Now that the panel is sized appropriately, you can paint the image by over-

riding

paintComponent( ):

public void paintComponent(Graphics g) {

g.drawImage(img,0,0,null);

}

It’s important to override paintComponent( ) instead of

paint( ), or else the child components won’t get drawn.

To test it, Example 1-2 uses an ImagePanel and the usual JFrame.

When run, the

ImageTest program looks like Figure 1-2.

Now that the background is done, it’s time to focus on the label, Activate

Reactor. This is just a static image that sits at a certain position on the back-

ground. You could use another

ImagePanel, but since the Activate Reactor

text is logically a

JLabel, you can just create an ImageLabel subclass, as

shown in Example 1-3.

Example 1-2. Testing out image-based panels

public class ImageTest {

public static void main(String[] args) {

ImagePanel panel = new ImagePanel(new

ImageIcon("images/background.png").getImage( ));

JFrame frame = new JFrame("Hack #1: Create Image-Themed Components");

frame.getContentPane( ).add(panel);

frame.pack( );

frame.setVisible(true);

}

}