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JLabel
Posted on: July 22, 2006 at 12:00 AM
Labels display fixed text or images on a GUI as information to the user.

Java: JLabel

 

Learn how to display fixed text or images with JLable component.

 

Labels display fixed text or images on a GUI as information to the user, for example, as a label in front of a a JTextField, etc.

 

You can have text (including HTML), an image, or both on a JLabel. A JLabel has a transparent background, so it will always match the container it is in.

JLabel Constructors

 

Here we are discussing about the JLabel constructors.

 

Assume the following declarations.

 

 

   String text;
   Icon   image;
   int    alignment; // JLabel.LEFT, JLabel.Center, or JLabel.RIGHT.
   
JLabel yourLabel = new JLabel(text);
JLabel yourLabel = new JLabel(text, alignment);
JLabel yourLabel = new JLabel(image);
JLabel yourLabel = new JLabel(image, alignment);
JLabel yourLabel = new JLabel(text, image, alignment);

 

Java Idiom

 

Because there is usually no need to refer to a JLabel after it has been added to a container, it is common to combine creation and adding the JLabel in one statement. For example.

p.add(new JLabel("Enter your ID:", JLabel.RIGHT));

is the same as

JLabel idLabel = new JLabel("Enter your ID:", JLabel.RIGHT);
. . .
p.add(idLabel);

HTML in JLabels

You may put HTML text in a JLabel. In this case the text should begin with <html> and end with </html>.

JLabel font and color

The most user-friendly interfaces are usually obtained by using the default appearance (font, color, background), but there are cases where you want to change these.

Appearance: setting the font

The font of a JLabel can be changed like this.

JLabel title = new JLabel("Want a Raise?", JLabel.CENTER);
title.setFont(new Font("Serif", Font.BOLD, 48));

Appearance: setting the text color

Use the setForeground method to set the text color.

JLabel title = new JLabel("Want a Raise?", JLabel.CENTER);
title.setForeground(Color.white);

Appearance: setting the background color

Because a JLabel's background is transparent, there is no effect from using the setBackground method. To make a new background, you need to create a JPanel with the appropriate color and put the label on that. For example

JLabel title = new JLabel("Want a Raise?");
title.setForeground(Color.white);
JPanel titlePanel = new JPanel();
titlePanel.setBackground(Color.blue);
titlePanel.add(title);  // adds to center of panel's default BorderLayout.

JLabel for output

Why using JLabel for output is usually bad

It's possible to change the text of a JLabel, although this is not generally a good idea after the user interface is already displayed. For output JTextField is often a better choice. The use of JLabel for output is mentioned because some textbooks display output this way. Here are some reasons not to use it.

  • Can't copy to clipboard. The user can not copy text from a JLabel, but can from a JTextField.
  • Can't set background. Changing the background of individual components probably isn't a good idea, so this restriction on JLabels is not serious. You can change the background of a JTextField, for better or worse.
  • Text length. This is where there are some serious issues. You can always see the entire text in a JTextField, altho you might have to scroll it it's long. There are several possibilities with a JLabel. You may either not see all of the long text in a JLabel, or putting long text into a JLabel may cause the layout to be recomputed, resulting in a truly weird user experience.

Changing the text of a JLabel

Most JLabels are never changed, except for internationalization, and that is done before the user interface is shown. To change the text, use

yourLabel.setText(String newText);  // 
Copyleft 2005 Fred Swartz MIT License
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