Class java.awt.CheckboxMenuItem - JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

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Class java.awt.CheckboxMenuItem

java.lang.Object
   |
   +----java.awt.MenuComponent
           |
           +----java.awt.MenuItem
                   |
                   +----java.awt.CheckboxMenuItem

public class CheckboxMenuItem
extends MenuItem
implements ItemSelectable

This class represents a check box that can be included in a menu. Clicking on 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:

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.

See Also:: ItemEvent, ItemListener

CheckboxMenuItem(): Create a check box menu item with an empty label.
CheckboxMenuItem(String): Create a check box menu item with the specified label.
CheckboxMenuItem(String, boolean): Create a check box menu item with the specified label and state.

addItemListener(ItemListener): Adds the specified item listener to receive item events from this check box menu item.
addNotify(): Creates the peer of the checkbox item.
getSelectedObjects(): Returns the an array (length 1) containing the checkbox menu item label or null if the checkbox is not selected.
getState(): Determines whether the state of this check box menu item is "on" or "off."
paramString(): Returns the parameter string representing the state of this check box menu item.
processEvent(AWTEvent): Processes events on this check box menu item.
processItemEvent(ItemEvent): Processes item events occurring on this check box menu item by dispatching them to any registered ItemListener objects.
removeItemListener(ItemListener): Removes the specified item listener so that it no longer receives item events from this check box menu item.
setState(boolean): Sets this check box menu item to the specifed state.

CheckboxMenuItem

 public CheckboxMenuItem()

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

CheckboxMenuItem

 public CheckboxMenuItem(String label)

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.

CheckboxMenuItem

 public CheckboxMenuItem(String label,
                         boolean state)

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

Parameters:: label - the button label.; state - the initial state of the menu item, where true indicates "on" and false indicates "off."

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:: createCheckboxMenuItem, 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

setState

 public synchronized void setState(boolean b)

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

Parameters:: b - the boolean state of this check box menu item.
See Also:: getState

getSelectedObjects

 public synchronized Object[] getSelectedObjects()

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

See Also:: ItemSelectable

addItemListener

 public synchronized void addItemListener(ItemListener l)

Adds the specified item listener to receive item events from this check box menu item.

Parameters:: l - the item listener.
See Also:: ItemEvent, ItemListener, removeItemListener

removeItemListener

 public synchronized void removeItemListener(ItemListener l)

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

Parameters:: l - the item listener.
See Also:: ItemEvent, ItemListener, addItemListener

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.

Parameters:: e - the event
Overrides:: processEvent in class MenuItem
See Also:: ItemEvent, processItemEvent

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.

Parameters:: e - the item event.
See Also:: ItemEvent, ItemListener, addItemListener, enableEvents

paramString

 public String paramString()

Returns the parameter string representing the state of this check box menu item. This string is useful for debugging.

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

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