public class Checkbox
extends Component
implements ItemSelectable, Accessible

A check box is a graphical component that can be in either an "on" (true) or "off" (false) state. Clicking on a check box changes its state from "on" to "off," or from "off" to "on."

The following code example creates a set of check boxes in a grid layout:

 setLayout(new GridLayout(3, 1));
 add(new Checkbox("one", null, true));
 add(new Checkbox("two"));
 add(new Checkbox("three"));
 

This image depicts the check boxes and grid layout created by this code example:

The button labeled one is in the "on" state, and the other two are in the "off" state. In this example, which uses the GridLayout class, the states of the three check boxes are set independently.

Alternatively, several check boxes can be grouped together under the control of a single object, using the CheckboxGroup class. In a check box group, at most one button can be in the "on" state at any given time. Clicking on a check box to turn it on forces any other check box in the same group that is on into the "off" state.

public Checkbox()

Creates a check box with an empty string for its label. The state of this check box is set to "off," and it is not part of any check box group.

HeadlessException: if GraphicsEnvironment.isHeadless() returns true

public Checkbox(String)

Creates a check box with the specified label. The state of this check box is set to "off," and it is not part of any check box group.

String label: a string label for this check box, or null for no label.

HeadlessException: if GraphicsEnvironment.isHeadless returns true

public Checkbox(String, boolean)

Creates a check box with the specified label and sets the specified state. This check box is not part of any check box group.

String label: a string label for this check box, or null for no label

boolean state: the initial state of this check box

HeadlessException: if GraphicsEnvironment.isHeadless returns true

public Checkbox(String, boolean, CheckboxGroup)

Constructs a Checkbox with the specified label, set to the specified state, and in the specified check box group.

String label: a string label for this check box, or null for no label.

boolean state: the initial state of this check box.

CheckboxGroup group: a check box group for this check box, or null for no group.

HeadlessException: if GraphicsEnvironment.isHeadless returns true

public Checkbox(String, CheckboxGroup, boolean)

Creates a check box with the specified label, in the specified check box group, and set to the specified state.

String label: a string label for this check box, or null for no label.

CheckboxGroup group: a check box group for this check box, or null for no group.

boolean state: the initial state of this check box.

HeadlessException: if GraphicsEnvironment.isHeadless returns true

public synchronized void addItemListener(ItemListener)

Adds the specified item listener to receive item events from this check box. Item events are sent to listeners in response to user input, but not in response to calls to setState(). If l is null, no exception is thrown and no action is performed.

Refer to AWT Threading Issues for details on AWT's threading model.

ItemListener l: the item listener

public void addNotify()

Creates the peer of the Checkbox. The peer allows you to change the look of the Checkbox without changing its functionality.

public AccessibleContext getAccessibleContext()

Gets the AccessibleContext associated with this Checkbox. For checkboxes, the AccessibleContext takes the form of an AccessibleAWTCheckbox. A new AccessibleAWTCheckbox is created if necessary.

public CheckboxGroup getCheckboxGroup()

Determines this check box's group.

public synchronized ItemListener getItemListeners()

Returns an array of all the item listeners registered on this checkbox.

public String getLabel()

Gets the label of this check box.

public EventListener getListeners(Class)

Returns an array of all the objects currently registered as FooListeners upon this Checkbox. FooListeners are registered using the addFooListener method.

You can specify the listenerType argument with a class literal, such as FooListener.class. For example, you can query a Checkbox c for its item listeners with the following code:

ItemListener[] ils = (ItemListener[])(c.getListeners(ItemListener.class));

java.lang.Class listenerType: the type of listeners requested; this parameter should specify an interface that descends from java.util.EventListener

ClassCastException: if listenerType doesn't specify a class or interface that implements java.util.EventListener

public Object getSelectedObjects()

Returns an array (length 1) containing the checkbox label or null if the checkbox is not selected.

public boolean getState()

Determines whether this check box is in the "on" or "off" state. The boolean value true indicates the "on" state, and false indicates the "off" state.

protected String paramString()

Returns a string representing the state of this Checkbox. This method is intended to be used only for debugging purposes, and the content and format of the returned string may vary between implementations. The returned string may be empty but may not be null.

protected void processEvent(AWTEvent)

Processes events on this check box. If the event is an instance of ItemEvent, this method invokes the processItemEvent method. Otherwise, it calls its superclass's processEvent method.

Note that if the event parameter is null the behavior is unspecified and may result in an exception.

AWTEvent e: the event

protected void processItemEvent(ItemEvent)

Processes item events occurring on this check box by dispatching them to any registered ItemListener objects.

This method is not called unless item events are enabled for this component. Item events are enabled when one of the following occurs:

• An ItemListener object is registered via addItemListener.
• Item events are enabled via enableEvents.

Note that if the event parameter is null the behavior is unspecified and may result in an exception.

ItemEvent e: the item event

public synchronized void removeItemListener(ItemListener)

Removes the specified item listener so that the item listener no longer receives item events from this check box. If l is null, no exception is thrown and no action is performed.

Refer to AWT Threading Issues for details on AWT's threading model.

ItemListener l: the item listener

public void setCheckboxGroup(CheckboxGroup)

Sets this check box's group to the specified check box group. If this check box is already in a different check box group, it is first taken out of that group.

If the state of this check box is true and the new group already has a check box selected, this check box's state is changed to false. If the state of this check box is true and the new group has no check box selected, this check box becomes the selected checkbox for the new group and its state is true.

CheckboxGroup g: the new check box group, or null to remove this check box from any check box group

public void setLabel(String)

Sets this check box's label to be the string argument.

String label: a string to set as the new label, or null for no label.

public void setState(boolean)

Sets the state of this check box to the specified state. The boolean value true indicates the "on" state, and false indicates the "off" state.

Note that this method should be primarily used to initialize the state of the checkbox. Programmatically setting the state of the checkbox will not trigger an ItemEvent. The only way to trigger an ItemEvent is by user interaction.

boolean state: the boolean state of the check box