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ButtonGroup.javaAPI DocJava SE 5 API5095Fri Aug 26 14:57:52 BST 2005javax.swing

ButtonGroup

public class ButtonGroup extends Object implements Serializable
This class is used to create a multiple-exclusion scope for a set of buttons. Creating a set of buttons with the same ButtonGroup object means that turning "on" one of those buttons turns off all other buttons in the group.

A ButtonGroup can be used with any set of objects that inherit from AbstractButton. Typically a button group contains instances of JRadioButton, JRadioButtonMenuItem, or JToggleButton. It wouldn't make sense to put an instance of JButton or JMenuItem in a button group because JButton and JMenuItem don't implement the selected state.

Initially, all buttons in the group are unselected. Once any button is selected, one button is always selected in the group. There is no way to turn a button programmatically to "off", in order to clear the button group. To give the appearance of "none selected", add an invisible radio button to the group and then programmatically select that button to turn off all the displayed radio buttons. For example, a normal button with the label "none" could be wired to select the invisible radio button.

For examples and further information on using button groups see How to Use Radio Buttons, a section in The Java Tutorial.

Warning: Serialized objects of this class will not be compatible with future Swing releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Swing. As of 1.4, support for long term storage of all JavaBeansTM has been added to the java.beans package. Please see {@link java.beans.XMLEncoder}.

version
1.37 05/05/04
author
Jeff Dinkins

Fields Summary
protected Vector
buttons
ButtonModel
selection
The current selection.
Constructors Summary
public ButtonGroup()
Creates a new ButtonGroup.
Methods Summary
public voidadd(javax.swing.AbstractButton b)
Adds the button to the group.

param
b the button to be added

        if(b == null) {
            return;
        }
        buttons.addElement(b);

        if (b.isSelected()) {
            if (selection == null) {
                selection = b.getModel();
            } else {
                b.setSelected(false);
            }
        }

        b.getModel().setGroup(this);
public intgetButtonCount()
Returns the number of buttons in the group.

return
the button count
since
1.3

	if (buttons == null) {
	    return 0;
	} else {
	    return buttons.size();
	}
public java.util.EnumerationgetElements()
Returns all the buttons that are participating in this group.

return
an Enumeration of the buttons in this group

        return buttons.elements();
public javax.swing.ButtonModelgetSelection()
Returns the model of the selected button.

return
the selected button model

        return selection;
public booleanisSelected(javax.swing.ButtonModel m)
Returns whether a ButtonModel is selected.

return
true if the button is selected, otherwise returns false

        return (m == selection);
public voidremove(javax.swing.AbstractButton b)
Removes the button from the group.

param
b the button to be removed

        if(b == null) {
            return;
        }
        buttons.removeElement(b);
        if(b.getModel() == selection) {
            selection = null;
        }
        b.getModel().setGroup(null);
public voidsetSelected(javax.swing.ButtonModel m, boolean b)
Sets the selected value for the ButtonModel. Only one button in the group may be selected at a time.

param
m the ButtonModel
param
b true if this button is to be selected, otherwise false

        if (b && m != null && m != selection) {
            ButtonModel oldSelection = selection;
            selection = m;
            if (oldSelection != null) {
                oldSelection.setSelected(false);
            }
            m.setSelected(true);
        }