JLabel : Java Glossary

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JLabel

is a component used to display decorative text on the screen to label some other component. The user cannot ever modify the text, unlike JTextfields. In AWT (Advanced Windowing Toolkit) you use Label, in Swing JLabel. JLabel.setHorizonalAlignment ( JLabel. LEFT ) or JLabel.setHorizonalAlignment ( JLabel. RIGHT ) lets you control the justification or the shortcut specification in the constructor. You control positioning of the text within the JLabel with setHorizonalAlignment and setVerticalAlignment and with setBorder.

Gotchas

The background colour setBackground() is ignored unless you do a setOpaque( true ).
Unlike a JTextField, you don’t use setContentType( text/html ) to embed HTML (Hypertext Markup Language) in the text.

Multiline Labels

If you embed \ns in the text of JLabels they will be treated like spaces. You can’t use \ns to create multi-line labels.
You can embed HTML in the text of a JLabel to get a multi-line JLabel. This is the easiest way to get a multi-line label. The main drawback is using it causes the entire HTML-rendering mechanism to be loaded. Also sometimes JLabels mysteriously reshape themselves to tall skinny rectangles with only a few words per line. This technique thanks to a tip from Eitan Rosenberg:

You can use a JTextArea to fake a multi-line JLabel. Set the background colour to the body colour of the whole application to simulate transparency.

// fake multi-line JLabel with JTextArea
final JTextArea jta = new JTextArea();
jta.setFont( new Font( "Dialog", Font.PLAIN, 12 ) );
jta.setForeground( FOREGROUND_FOR_INSTRUCTIONS );
jta.setBackground( BACKGROUND_FOR_BODY );
jta.setEditable( false );
jta.setBorder( BorderFactory.createEmptyBorder() );
jta.setText( "line1\nline2");

You can embed <br> and other simple HTML markup with a JEditorPane like this:

Unfortunately, Oracle does not document just what features of HTML are supported. I discovered by experiment the entity ⇒ is not supported. The renderer does not insist on <body>…</body> tags. I have discovered that JEditorPanes accept <style commands. I have written Oracle asking them to clarify.

Learning More

Oracle’s Javadoc on JLabel class : available:

on the web at Oracle.com
in the current JDK 1.8.0_131 on your local Windows J: drive.

Oracle’s Miscellaneous documentation on Jlabel

Oracle’s Miscellaneous documentation on Using HTML in JLabels and other components

AWT
JEditorPane
JTextField
Label
layout
margin
setOpaque
Swing

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