Java: JLabel

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

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);
. . .

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);

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?");
JPanel titlePanel = new JPanel();
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.

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);  //