Class CheckboxMenuItem

All Implemented Interfaces:
ItemSelectable, Serializable, Accessible 
public class CheckboxMenuItem
extends MenuItem
implements ItemSelectable, Accessible

This class represents a check box that can be included in a menu. Selecting the check box in the menu changes its state from "on" to "off" or from "off" to "on."

The following picture depicts a menu which contains an instance of CheckBoxMenuItem:

Menu labeled Examples, containing items Basic, Simple, Check, and More Examples. The Check item is a CheckBoxMenuItem instance, in the off state.

The item labeled Check shows a check box menu item in its "off" state.

When a check box menu item is selected, AWT sends an item event to the item. Since the event is an instance of ItemEvent, the processEvent method examines the event and passes it along to processItemEvent. The latter method redirects the event to any ItemListener objects that have registered an interest in item events generated by this menu item.

Since:
1.0
See Also:
ItemEvent, ItemListener, Serialized Form

Nested Class Summary

Nested Classes
Modifier and Type Class Description
protected class  CheckboxMenuItem.AccessibleAWTCheckboxMenuItem

Inner class of CheckboxMenuItem used to provide default support for accessibility.

Nested classes/interfaces declared in class java.awt.MenuItem

MenuItem.AccessibleAWTMenuItem

Nested classes/interfaces declared in class java.awt.MenuComponent

MenuComponent.AccessibleAWTMenuComponent

Constructor Summary

Constructors
Constructor Description
CheckboxMenuItem()

Create a check box menu item with an empty label.
CheckboxMenuItem​(String label)

Create a check box menu item with the specified label.
CheckboxMenuItem​(String label, boolean state)

Create a check box menu item with the specified label and state.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type Method Description
void addItemListener​(ItemListener l)

Adds the specified item listener to receive item events from this check box menu item.
void addNotify()

Creates the peer of the checkbox item.
AccessibleContext getAccessibleContext()

Gets the AccessibleContext associated with this CheckboxMenuItem.
ItemListener[] getItemListeners()

Returns an array of all the item listeners registered on this checkbox menuitem.
<T extends EventListener>
T[]		 getListeners​(Class<T> listenerType)

Returns an array of all the objects currently registered as FooListeners upon this CheckboxMenuItem.
Object[] getSelectedObjects()

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

Determines whether the state of this check box menu item is "on" or "off."
String paramString()

Returns a string representing the state of this CheckBoxMenuItem.
protected void processEvent​(AWTEvent e)

Processes events on this check box menu item.
protected void processItemEvent​(ItemEvent e)

Processes item events occurring on this check box menu item by dispatching them to any registered ItemListener objects.
void removeItemListener​(ItemListener l)

Removes the specified item listener so that it no longer receives item events from this check box menu item.
void setState​(boolean b)

Sets this check box menu item to the specified state.

Methods declared in class java.awt.MenuItem

addActionListener, deleteShortcut, disable, disableEvents, enable, enable, enableEvents, getActionCommand, getActionListeners, getLabel, getShortcut, isEnabled, processActionEvent, removeActionListener, setActionCommand, setEnabled, setLabel, setShortcut

Methods declared in class java.awt.MenuComponent

dispatchEvent, getFont, getName, getParent, getTreeLock, postEvent, removeNotify, setFont, setName, toString

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

CheckboxMenuItem

public CheckboxMenuItem()
                 throws HeadlessException

Create a check box menu item with an empty label. The item's state is initially set to "off."

Throws:
HeadlessException - if GraphicsEnvironment.isHeadless() returns true
Since:
1.1
See Also:
GraphicsEnvironment.isHeadless()

CheckboxMenuItem

public CheckboxMenuItem​(String label)
                 throws HeadlessException

Create a check box menu item with the specified label. The item's state is initially set to "off."

Parameters:
label - a string label for the check box menu item, or null for an unlabeled menu item.
Throws:
HeadlessException - if GraphicsEnvironment.isHeadless() returns true
See Also:
GraphicsEnvironment.isHeadless()

CheckboxMenuItem

public CheckboxMenuItem​(String label,
                        boolean state)
                 throws HeadlessException

Create a check box menu item with the specified label and state.

Parameters:
label - a string label for the check box menu item, or null for an unlabeled menu item.
state - the initial state of the menu item, where true indicates "on" and false indicates "off."
Throws:
HeadlessException - if GraphicsEnvironment.isHeadless() returns true
Since:
1.1
See Also:
GraphicsEnvironment.isHeadless()

Method Detail

addNotify

public void addNotify()

Creates the peer of the checkbox item. This peer allows us to change the look of the checkbox item without changing its functionality. Most applications do not call this method directly.

Overrides:
addNotify in class MenuItem
See Also:
Component.getToolkit()

getState

public boolean getState()

Determines whether the state of this check box menu item is "on" or "off."

Returns:
the state of this check box menu item, where true indicates "on" and false indicates "off"
See Also:
setState(boolean)

setState

public void setState​(boolean b)

Sets this check box menu item to the specified state. The boolean value true indicates "on" while false indicates "off."

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

Parameters:
b - true if the check box menu item is on, otherwise false
See Also:
getState()

getSelectedObjects

public Object[] getSelectedObjects()

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

Specified by:
getSelectedObjects in interface ItemSelectable
Returns:
the list of selected objects, or null
See Also:
ItemSelectable

addItemListener

public void addItemListener​(ItemListener l)

Adds the specified item listener to receive item events from this check box menu item. Item events are sent in response to user actions, 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.

Specified by:
addItemListener in interface ItemSelectable
Parameters:
l - the item listener
Since:
1.1
See Also:
removeItemListener(java.awt.event.ItemListener), getItemListeners(), setState(boolean), ItemEvent, ItemListener

removeItemListener

public void removeItemListener​(ItemListener l)

Removes the specified item listener so that it no longer receives item events from this check box menu item. 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.

Specified by:
removeItemListener in interface ItemSelectable
Parameters:
l - the item listener
Since:
1.1
See Also:
addItemListener(java.awt.event.ItemListener), getItemListeners(), ItemEvent, ItemListener

getItemListeners

public ItemListener[] getItemListeners()

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

Returns:
all of this checkbox menuitem's ItemListeners or an empty array if no item listeners are currently registered
Since:
1.4
See Also:
addItemListener(java.awt.event.ItemListener), removeItemListener(java.awt.event.ItemListener), ItemEvent, ItemListener

getListeners

public <T extends EventListener> T[] getListeners​(Class<T> listenerType)

Returns an array of all the objects currently registered as FooListeners upon this CheckboxMenuItem. 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 CheckboxMenuItem c for its item listeners with the following code: 

ItemListener[] ils = (ItemListener[])(c.getListeners(ItemListener.class));
If no such listeners exist, this method returns an empty array.
Overrides:
getListeners in class MenuItem
Type Parameters:
T - the type of the listeners
Parameters:
listenerType - the type of listeners requested; this parameter should specify an interface that descends from java.util.EventListener
Returns:
an array of all objects registered as FooListeners on this checkbox menuitem, or an empty array if no such listeners have been added
Throws:
ClassCastException - if listenerType doesn't specify a class or interface that implements java.util.EventListener
Since:
1.3
See Also:
getItemListeners()

processEvent

protected void processEvent​(AWTEvent e)

Processes events on this check box menu item. If the event is an instance of ItemEvent, this method invokes the processItemEvent method. If the event is not an item event, it invokes processEvent on the superclass.

Check box menu items currently support only item events.

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

Overrides:
processEvent in class MenuItem
Parameters:
e - the event
Since:
1.1
See Also:
ItemEvent, processItemEvent(java.awt.event.ItemEvent)

processItemEvent

protected void processItemEvent​(ItemEvent e)

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

This method is not called unless item events are enabled for this menu item. 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.

Parameters:
e - the item event
Since:
1.1
See Also:
ItemEvent, ItemListener, addItemListener(java.awt.event.ItemListener), MenuItem.enableEvents(long)

paramString

public String paramString()

Returns a string representing the state of this CheckBoxMenuItem. 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.

Overrides:
paramString in class MenuItem
Returns:
the parameter string of this check box menu item

getAccessibleContext

public AccessibleContext getAccessibleContext()

Gets the AccessibleContext associated with this CheckboxMenuItem. For checkbox menu items, the AccessibleContext takes the form of an AccessibleAWTCheckboxMenuItem. A new AccessibleAWTCheckboxMenuItem is created if necessary.

Specified by:
getAccessibleContext in interface Accessible
Overrides:
getAccessibleContext in class MenuItem
Returns:
an AccessibleAWTCheckboxMenuItem that serves as the AccessibleContext of this CheckboxMenuItem
Since:
1.3