How to Use Borders

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

Note: Our examples set borders on JPanels , JLabels , and custom subclasses of JComponent . Although technically you can set the border on any object that inherits from JComponent , the look-and-feel implementation of many standard Swing components doesn't work well with user -set borders. In general, when you want to set a border on a standard Swing component other than JPanel or JLabel , put the component in a JPanel and set the border on the JPanel . The GTK+ look and feel handles borders differently than do other look and feels. Please refer to the v1.4.2 release notes for details: http://java.sun.com/j2se/1.4.2/relnotes.html.

To put a border around a JComponent , use its setBorder method. You can use the BorderFactory ^[15] 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 ”save it in a variable of type Border . ^[16] Here's an example of code that creates a bordered container:

^[15] BorderFactory API documentation: http://java.sun.com/j2se/1.4.2/docs/api/javax/swing/BorderFactory.html.

^[16] Border API documentation: http://java.sun.com/j2se/1.4.2/docs/api/javax/swing/Border.html.

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

Figure 8 is a picture of the container that contains a label component. The black line drawn by the border marks the edge of the container.

Figure 8. A simple line border on a label.

The BorderDemo Example

Figures 9 through 12 show an application called BorderDemo that displays the borders Swing provides. Figure 9 illustrates the simple border types. The code for creating these borders is provided in Using the Borders Provided by Swing (page 539).

Figure 9. A screenshot of several simple borders shown on the Simple tab of BorderDemo .

Figure 12. A screenshot of several compound borders shown on the Compound tab of BorderDemo .

You can run BorderDemo using Java Web Start or compile and run the example yourself. ^[17]

^[17] To run BorderDemo using Java Web Start, click the BorderDemo link on the RunExamples/misc.html page on the CD. You can find the source files here: JavaTutorial/uiswing/misc/example-1dot4/index.html#BorderDemo .

Figure 10 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 border to paint. Be careful when choosing the icon and determining your component's size ; otherwise , the icon might get chopped off or be mismatched at the component's corners.

Figure 10. A screenshot of several matte borders shown on the Matte tab of BorderDemo .

Figure 11 shows titled borders.A titled border 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 is a gray line whereas the default titled border in the Windows look and feel is etched. By default, the title straddles the upper left of the border, as shown at the top of Figure 11.

Figure 11. A screenshot of several titled borders shown on the Titled tab of BorderDemo .

Figure 12 shows compound borders. With these, 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 that you saw in the preceding figures.

 //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. BorderFactory , 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 package javax.swing.border . ^[18] You often don't need to directly use anything in the border package, except when specifying constants specific to a particular border class or when referring to the Border type.

^[18] javax.swing.border API documentation: http://java.sun.com/j2se/1.4.2/docs/api/javax/swing/border/package-summary.html.

Creating Custom Borders

If BorderFactory doesn't offer you enough control over a border's form, you might need to 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 in Figures 9 through 12: LineBorder , EtchedBorder , BevelBorder , EmptyBorder , MatteBorder , TitledBorder , and CompoundBorder . It 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, generally by creating a subclass of the AbstractBorder ^[19] class. In your subclass, you must implement at least one constructor and the following two methods :

^[19] AbstractBorder API documentation: http://java.sun.com/j2se/1.4.2/docs/api/javax/swing/border/AbstractBorder.html.

• paintBorder , which contains the painting code that a JComponent executes to paint the border.

• getBorderInsets , which specifies the amount of space the border needs to paint itself.

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

The Border API

Tables 7 and 8 list the commonly used border methods. BorderFactory API documentation is at: http://java.sun.com/j2se/1.4.2/docs/api/javax/swing/BorderFactory.html. The rest of the border- related classes and interfaces are in the border package, which is documented at: http://java.sun.com/j2se/1.4.2/docs/api/javax/swing/border/package-summary.html.

Table 7. Creating a Border with BorderFactory

Method	Purpose
Border createLineBorder(Color) Border createLineBorder(Color, int)	Create a line border. The first argument is a java.awt.Color object that specifies the color of the line. The optional second argument specifies the width of the line in pixels.
Border createEtchedBorder() Border createEtchedBorder(Color, Color) Border createEtchedBorder(int) Border createEtchedBorder(int, Color, Color)	Create an etched border. The optional Color arguments specify the highlight and shadow colors to be used. In release 1.3, methods with int arguments were added that allow the border methods to be specified as either EtchedBorder.RAISED or EtchedBorder.LOWERED . The methods without the int arguments create a lowered etched border.
Border createLoweredBevelBorder()	Create a border that gives the illusion of the component being lower than the surrounding area.
Border createRaisedBevelBorder()	Create a border that gives the illusion of the component being higher than the surrounding area.
Border createBevelBorder(int, Color, Color) Border createBevelBorder(int, Color, Color, Color, Color)	Create a raised or lowered beveled border, specifying the colors to use. The integer argument can be either BevelBorder.RAISED or BevelBorder.LOWERED . With the three-argument constructor, you specify the highlight and shadow colors. With the five-argument constructor, you specify outer highlight, inner highlight, outer shadow, and inner shadow colors, in that order. The shadow inner and outer colors are switched for a lowered bevel border.
Border createEmptyBorder() Border createEmptyBorder(int, int, int, int)	Create an invisible border. If you specify no arguments, the border takes no space, which is useful when creating a titled border with no visible boundary. The optional arguments specify the number of pixels that the border occupies at the top, left, bottom, and right (in that order) of whatever component uses it. This method is useful for putting empty space around components.
MatteBorder createMatteBorder(int, int, int, int, Color) MatteBorder createMatteBorder(int, int, int, int, Icon)	Create a matte border. The integer arguments specify the number of pixels that the border occupies at the top, left, bottom, and right (in that order) of whatever component uses it. The color argument specifies the color with which the border should fill its area. The icon argument specifies the icon with which the border should tile its area.
TitledBorder createTitledBorder(String) TitledBorder createTitledBorder(Border) TitledBorder createTitledBorder( Border, String) TitledBorder createTitledBorder( Border, String, int, int) TitledBorder createTitledBorder( Border, String, int, int, Font) TitledBorder createTitledBorder( Border, String, int, int, Font, Color)	Create a titled border. The string argument specifies the title to be displayed. The optional font and color arguments specify the font and color to be used for the title's text. The border argument specifies the border that should be displayed along with the title. If no border is specified, a look-and-feel-specific default border is used. By default, the title straddles the top of its companion border and is left-justified. The optional integer arguments specify the title's position and justification, in that order. TitledBorder defines these possible positions : ABOVE_TOP , TOP (the default), BELOW_TOP , ABOVE_BOTTOM , BOTTOM , and BELOW_BOTTOM . You can specify the justification as LEADING (the default), CENTER , or TRAILING . In locales with Western alphabets, LEADING is equivalent to LEFT and TRAILING is equivalent to RIGHT .
CompoundBorder createCompoundBorder(Border, Border)	Combine two borders into one. The first argument specifies the outer border; the second, the inner border.

Examples That Use Borders

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

Example	Where Described	Notes
BorderDemo	This section	Shows an example of each type of border that BorderFactory can create. Also uses an empty border to add breathing space between each pane and its contents.
AlignmentDemo	How to Use BoxLayout (page 462)	Uses titled borders.
BoxLayoutDemo	How to Use BoxLayout (page 462)	Uses a red line to show where the edge of a container is so that you can see how the extra space in a box layout is distributed.
ComboBoxDemo2	How to Use Combo Boxes (page 176)	Uses a compound border to combine a line border with an empty border. The empty border provides space between the line and the component's innards.