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Every JComponent can have one or more borders. Borders are incredibly useful objects that, while not themselves components, know how to draw the edges of Swing components. Borders are useful not only for drawing lines and fancy edges, but also for providing titles and empty space around components.

To put a border around a JComponent, you use its setBorder method. You can use the BorderFactory class to create most of the borders that Swing provides. If you need a reference to a border — say, because you want to use it in multiple components — you can save it in a variable of type Border. Here is an example of code that creates a bordered container:

JPanel pane = new JPanel();
pane.setBorder(BorderFactory.createLineBorder(Color.black));

Here's a picture of the container, which contains a label component. The black line drawn by the border marks the edge of the container.

The rest of this page discusses the following topics:

• The BorderDemo Example
• Using the Borders Provided by Swing
• Creating Custom Borders
• The Border API
• Examples of Using Borders

The BorderDemo Example

The following pictures show an application called BorderDemo that displays the borders Swing provides. We show the code for creating these borders a little later, in Using the Borders Provided by Swing.

Click the Launch button to run the BorderDemo example using Java™ Web Start (download JDK 7 or later). Alternatively, to compile and run the example yourself, consult the example index.

The next picture shows some matte borders. When creating a matte border, you specify how many pixels it occupies at the top, left, bottom, and right of a component. You then specify either a color or an icon for the matte border to draw. You need to be careful when choosing the icon and determining your component's size; otherwise, the icon might get chopped off or have mismatch at the component's corners.

The next picture shows titled borders. Using a titled border, you can convert any border into one that displays a text description. If you don't specify a border, a look-and-feel-specific border is used. For example, the default titled border in the Java look and feel uses a gray line, and the default titled border in the Windows look and feel uses an etched border. By default, the title straddles the upper left of the border, as shown at the top of the following figure.

The next picture shows compound borders. With compound borders, you can combine any two borders, which can themselves be compound borders.

Using the Borders Provided by Swing

The code that follows shows how to create and set the borders you saw in the preceding figures. You can find the program's code in BorderDemo.java.

//Keep references to the next few borders,
//for use in titles and compound borders.
Border blackline, raisedetched, loweredetched,
       raisedbevel, loweredbevel, empty;

blackline = BorderFactory.createLineBorder(Color.black);
raisedetched = BorderFactory.createEtchedBorder(EtchedBorder.RAISED);
loweredetched = BorderFactory.createEtchedBorder(EtchedBorder.LOWERED);
raisedbevel = BorderFactory.createRaisedBevelBorder();
loweredbevel = BorderFactory.createLoweredBevelBorder();
empty = BorderFactory.createEmptyBorder();

//Simple borders
jComp1.setBorder(blackline);
jComp2.setBorder(raisedbevel);
jComp3.setBorder(loweredbevel);
jComp4.setBorder(empty);

//Matte borders
ImageIcon icon = createImageIcon("images/wavy.gif",
                                 "wavy-line border icon"); //20x22

jComp5.setBorder(BorderFactory.createMatteBorder(
                                   -1, -1, -1, -1, icon));
jComp6.setBorder(BorderFactory.createMatteBorder(
                                    1, 5, 1, 1, Color.red));
jComp7.setBorder(BorderFactory.createMatteBorder(
                                    0, 20, 0, 0, icon));

//Titled borders
TitledBorder title;
title = BorderFactory.createTitledBorder("title");
jComp8.setBorder(title);

title = BorderFactory.createTitledBorder(
                       blackline, "title");
title.setTitleJustification(TitledBorder.CENTER);
jComp9.setBorder(title);

title = BorderFactory.createTitledBorder(
                       loweredetched, "title");
title.setTitleJustification(TitledBorder.RIGHT);
jComp10.setBorder(title);

title = BorderFactory.createTitledBorder(
                       loweredbevel, "title");
title.setTitlePosition(TitledBorder.ABOVE_TOP);
jComp11.setBorder(title);

title = BorderFactory.createTitledBorder(
                       empty, "title");
title.setTitlePosition(TitledBorder.BOTTOM);
jComp12.setBorder(title);

//Compound borders
Border compound;
Border redline = BorderFactory.createLineBorder(Color.red);

//This creates a nice frame.
compound = BorderFactory.createCompoundBorder(
                          raisedbevel, loweredbevel);
jComp13.setBorder(compound);

//Add a red outline to the frame.
compound = BorderFactory.createCompoundBorder(
                          redline, compound);
jComp14.setBorder(compound);

//Add a title to the red-outlined frame.
compound = BorderFactory.createTitledBorder(
                          compound, "title",
                          TitledBorder.CENTER,
                          TitledBorder.BELOW_BOTTOM);
jComp15.setBorder(compound);

As you probably noticed, the code uses the BorderFactory class to create each border. The BorderFactory class, which is in the javax.swing package, returns objects that implement the Border interface.

The Border interface, as well as its Swing-provided implementations, is in the javax.swing.border package. You often don't need to directly use anything in the border package, except when specifying constants that are specific to a particular border class or when referring to the Border type.

Creating Custom Borders

If BorderFactory doesn't offer you enough control over a border's form, then you might need to directly use the API in the border package — or even define your own border. In addition to containing the Border interface, the border package contains the classes that implement the borders you've already seen: LineBorder, EtchedBorder, BevelBorder, EmptyBorder, MatteBorder, TitledBorder, and CompoundBorder. The border package also contains a class named SoftBevelBorder, which produces a result similar to BevelBorder, but with softer edges.

If none of the Swing borders is suitable, you can implement your own border. Generally, you do this by creating a subclass of the AbstractBorder class. In your subclass, you must implement at least one constructor and the following two methods:

• paintBorder, which contains the drawing code that a JComponent executes to draw the border.
• getBorderInsets, which specifies the amount of space the border needs to draw itself.

If a custom border has insets (and they typically have insets) you need to override both AbstractBorder.getBorderInsets(Component c) and AbstractBorder.getBorderInsets(Component c, Insets insets) to provide the correct insets.

For examples of implementing borders, see the source code for the classes in the javax.swing.border package.

The Border API

The following tables list the commonly used border methods. The API for using borders falls into two categories:

• Creating a Border with BorderFactory
• Setting or Getting a Component's Border

Examples that Use Borders

Many examples in this lesson use borders. The following table lists a few interesting cases.