CheckboxMenuItem (Java Platform SE 8 )
Keywords: java.awt.CheckboxMenuItem class
Date: 2017-07-29

java.awt

## Class CheckboxMenuItem

- java.lang.Object
- - java.awt.MenuComponent
  - - java.awt.MenuItem
    - - java.awt.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`:

  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:
    JDK1.0
  See Also:
    `ItemEvent`, `ItemListener`, Serialized Form

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `protected class` | `CheckboxMenuItem.AccessibleAWTCheckboxMenuItem` Inner class of CheckboxMenuItem used to provide default support for accessibility.

    - ### Nested classes/interfaces inherited from class java.awt.MenuItem

      `MenuItem.AccessibleAWTMenuItem`

    - ### Nested classes/interfaces inherited from class java.awt.MenuComponent

      `MenuComponent.AccessibleAWTMenuComponent`

  - ### Constructor Summary

    Constructors
    Constructor and 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 and 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 `FooListener`s 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 inherited from class java.awt.MenuItem

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

    - ### Methods inherited from class java.awt.MenuComponent

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

    - ### Methods inherited from 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:
        JDK1.1
      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:
        JDK1.1
      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:
        `Toolkit.createCheckboxMenuItem(java.awt.CheckboxMenuItem)`, `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`
      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:
        JDK1.1
      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:
        JDK1.1
      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 `ItemListener`s 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 `FooListener`s upon this `CheckboxMenuItem`. `FooListener`s 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`
      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 `FooListener`s 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:
        JDK1.1
      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:
        JDK1.1
      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

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