How to Use Borders
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.
Our examples set borders on
JLabel s, 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
JLabel , we recommend that you put the component in a
JPanel and set the border on the
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 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.
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.
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.
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
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
JComponentexecutes 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
The following tables list the commonly used border methods. The API for using borders falls into two categories:
Border createLineBorder(Color, int)
|Create a line border. The first argument is a |
Border createEtchedBorder(Color, Color)
Border createEtchedBorder(int, Color, Color)
|Create an etched border. The optional |
|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 |
Border createEmptyBorder(int, int, int, int)
|Create an invisible border. If you specify no arguments, then 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 your 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 which with the border should fill its area. The icon argument specifies the icon which with the border should tile its area.|
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, then 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:
|CompoundBorder createCompoundBorder(Border, Border)||Combine two borders into one. The first argument specifies the outer border; the second, the inner border.|
|Set or get the border of the receiving |
|Set or get whether the border of the component should be displayed.|
Many examples in this lesson use borders. The following table lists a few interesting cases.
|BorderDemo||This section||Shows an example of each type of border that |
|BoxAlignmentDemo||How to Use BoxLayout||Uses titled borders.|
|BoxLayoutDemo||How to Use BoxLayout||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||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.|