Java: Radio Buttons

Radio buttons (javax.swing.JRadioButton) are used in groups (java.awt.ButtonGroup) where at most one can be selected. The example below produced this image. A radio button group starts with all buttons deselected, but after one is selected the only way to have them appear all off is to have an invisible button that is selected by the program.

Source code for above example

This example creates a group of three radio buttons, puts them in a grid layout on a panel, and puts a titled, etched border around them.

JRadioButton yesButton   = new JRadioButton("Yes"  , true);
JRadioButton noButton    = new JRadioButton("No"   , false);
JRadioButton maybeButton = new JRadioButton("Maybe", false);

ButtonGroup bgroup = new ButtonGroup();
bgroup.add(yesButton);
bgroup.add(noButton);
bgroup.add(maybeButton);

JPanel radioPanel = new JPanel();
radioPanel.setLayout(new GridLayout(3, 1));
radioPanel.add(yesButton);
radioPanel.add(noButton);
radioPanel.add(maybeButton);

radioPanel.setBorder(BorderFactory.createTitledBorder(
           BorderFactory.createEtchedBorder(), "Married?"));

Testing the status of radio buttons

There are several ways to find out about radio button states:

• During execution, test the radio button with isSelected().
• In the setup phase, add an action listener with addActionListener(...). ActionListeners are called when a radio button is selected.
• In the setup phase, add an item listener with addItemListener. ItemListeners are called both when the radio button is selected and (automatically) deselected.

JRadioButton methods

boolean b;
JRadioButton rb = new JRadioButton("Sample", false);

Common JRadioButton methods

b =	rb.isSelected();	Returns true if that button is selected.
	rb.setSelected(b);	Sets selected status of a radio button to b (true/false).
	rb.addActionListener(an-action-listener);	Adds an action listener to the radio button. The action listener will be called if button is selected.
	rb.addItemListener(an-item-listener);	Add an item listener to a radio button. The item listener will be called if the button is selected or deselected.

ButtonGroup methods

The most common method used for a button group is add(), but it's also possible to get or set the selected button. Assume:

JRadioButton rb = new JRadioButton("Sample", false);
ButtonGroup bgroup = new ButtonGroup();

Common ButtonGroup methods

	bgroup.add(rb);	Adds a button to a radio button group.
rb =	bgroup.getSelectedJRadioButton();	Returns the radio button which is currently selected.
	bgroup.setSelectedJRadioButton(rb);	Sets the status of a particular radio button (unsetting others).