How to Use Labels
With the JLabel class, you can display unselectable text and images. If you need to create a component that displays a string, an image, or both, you can do so by using or extending
JLabel . If the component is interactive and has a certain state, use a button instead of a label.
By specifying HTML code in a label's text, you can give the label various characteristics such as multiple lines, multiple fonts or multiple colors. If the label uses just a single color or font, you can avoid the overhead of HTML processing by using the
setFont method instead. See Using HTML in Swing Components for details.
Note that labels are not opaque by default. If you need to paint the label's background, it is recommended that you turn its opacity property to "true". The following code snippet shows how to do this.
The following picture introduces an application that displays three labels. The window is divided into three rows of equal height; the label in each row is as wide as possible.
Resize the window so you can see how the labels' contents are placed within the labels' drawing area.
All the label contents have default vertical alignment — that is, the label contents are centered vertically in the label's drawing area. The top label, which contains both an image and text, has horizontal center alignment. The second label, which contains just text, has left (leading) alignment, which is the default for text-only labels in left-to-right languages. The third label, which contains just an image, has horizontal center alignment, which is the default for image-only labels.
Below is the code from LabelDemo.java that creates the labels in the previous example.
ImageIcon icon = createImageIcon("images/middle.gif"); . . . label1 = new JLabel("Image and Text", icon, JLabel.CENTER); //Set the position of the text, relative to the icon: label1.setVerticalTextPosition(JLabel.BOTTOM); label1.setHorizontalTextPosition(JLabel.CENTER); label2 = new JLabel("Text-Only Label"); label3 = new JLabel(icon);
The code for the
createImageIcon method is similar to that used throughout this tutorial. You can find it in How to Use Icons.
Often, a label describes another component. When this occurs, you can improve your program's accessibility by using the
setLabelFor method to identify the component that the label describes. For example:
The preceding code, taken from the
FormattedTextFieldDemo example discussed in How to Use Formatted Text Fields, lets assistive technologies know that the label (
amountLabel ) provides information about the formatted text field (
amountField ). For more information about assistive technologies, see How to Support Assistive Technologies.
The following tables list the commonly used
JLabel constructors and methods. Other methods you are likely to call are defined by the
JComponent classes. They include
setOpaque , and
setBackground . See The JComponent Class for details. The API for using labels falls into three categories:
In the following API, do not confuse label alignment with X and Y alignment. X and Y alignment are used by layout managers and can affect the way any component — not just a label — is sized or positioned. Label alignment, on the other hand, has no effect on a label's size or position. Label alignment simply determines where, inside the label's painting area, the label's contents are positioned. Typically, the label's painting area is exactly the size needed to paint on the label and thus label alignment is irrelevant. For more information about X and Y alignment, see How to Use BoxLayout.
|Method or Constructor||Purpose|
JLabel(String, Icon, int)
|Creates a |
|Sets or gets the text displayed by the label. You can use HTML tags to format the text, as described in Using HTML in Swing Components.|
|Sets or gets the image displayed by the label.|
|Sets or gets the letter that should look like a keyboard alternative. This is helpful when a label describes a component (such as a text field) that has a keyboard alternative but cannot display it. If the labelFor property is also set (using |
|Sets or gets a hint as to which character in the text should be decorated to represent the mnemonic. This is useful when you have two instances of the same character and wish to decorate the second instance. For example, |
|Sets or gets the image displayed by the label when it is disabled. If you do not specify a disabled image, then the look and feel creates one by manipulating the default image.|
|Sets or gets the area on the label where its contents should be placed. The SwingConstants interface defines five possible values for horizontal alignment: |
|Sets or gets the location where the label's text will be placed, relative to the label's image. The SwingConstants interface defines five possible values for horizontal position: |
|Sets or gets the number of pixels between the label's text and its image.|
|Sets or gets which component the label describes.|
The following table lists some of the many examples that use labels.
|LabelDemo||This section||Shows how to specify horizontal and vertical alignment as well as how to align a label's text and image.|
|HtmlDemo||Using HTML in Swing Components||Lets you experiment with specifying HTML text for a label.|
|BoxAlignmentDemo||Fixing Alignment Problems||Demonstrates possible alignment problems when using a label in a vertical box layout. Shows how to solve the problem.|
|DialogDemo||How to Use Dialogs||Uses a changeable label to display instructions and provide feedback.|
|SplitPaneDemo||How to Use Split Panes and How to Use Lists||Displays an image using a label inside of a scroll pane.|
|SliderDemo2||How to Use Sliders||Uses |
|TableDialogEditDemo||How to Use Tables||Implements a label subclass, |
|FormattedTextFieldDemo||How to Use Formatted Text Fields||Has four rows, each containing a label and the formatted text field it describes.|
|TextComponentDemo||Text Component Features|
|ColorChooserDemo||How to Use Color Choosers||Uses an opaque label to display the currently chosen color against a fixed-color background.|
See the Using JavaFX UI Controls: Label tutorial to learn about JavaFX labeled controls.