Action (Java Platform SE 8 )
Keywords: javax.swing.Action interface
Date: 2020-03-26

javax.swing

## Interface Action

- All Superinterfaces:
    ActionListener, EventListener
  All Known Implementing Classes:
    AbstractAction, BasicDesktopPaneUI.CloseAction, BasicDesktopPaneUI.MaximizeAction, BasicDesktopPaneUI.MinimizeAction, BasicDesktopPaneUI.NavigateAction, BasicDesktopPaneUI.OpenAction, BasicFileChooserUI.ApproveSelectionAction, BasicFileChooserUI.CancelSelectionAction, BasicFileChooserUI.ChangeToParentDirectoryAction, BasicFileChooserUI.GoHomeAction, BasicFileChooserUI.NewFolderAction, BasicFileChooserUI.UpdateAction, BasicInternalFrameTitlePane.CloseAction, BasicInternalFrameTitlePane.IconifyAction, BasicInternalFrameTitlePane.MaximizeAction, BasicInternalFrameTitlePane.MoveAction, BasicInternalFrameTitlePane.RestoreAction, BasicInternalFrameTitlePane.SizeAction, BasicSliderUI.ActionScroller, BasicTreeUI.TreeCancelEditingAction, BasicTreeUI.TreeHomeAction, BasicTreeUI.TreeIncrementAction, BasicTreeUI.TreePageAction, BasicTreeUI.TreeToggleAction, BasicTreeUI.TreeTraverseAction, DefaultEditorKit.BeepAction, DefaultEditorKit.CopyAction, DefaultEditorKit.CutAction, DefaultEditorKit.DefaultKeyTypedAction, DefaultEditorKit.InsertBreakAction, DefaultEditorKit.InsertContentAction, DefaultEditorKit.InsertTabAction, DefaultEditorKit.PasteAction, HTMLEditorKit.HTMLTextAction, HTMLEditorKit.InsertHTMLTextAction, MetalFileChooserUI.DirectoryComboBoxAction, StyledEditorKit.AlignmentAction, StyledEditorKit.BoldAction, StyledEditorKit.FontFamilyAction, StyledEditorKit.FontSizeAction, StyledEditorKit.ForegroundAction, StyledEditorKit.ItalicAction, StyledEditorKit.StyledTextAction, StyledEditorKit.UnderlineAction, TextAction

      public interface Action
      extends ActionListener

  The `Action` interface provides a useful extension to the `ActionListener` interface in cases where the same functionality may be accessed by several controls.

  In addition to the `actionPerformed` method defined by the `ActionListener` interface, this interface allows the application to define, in a single place:

  - One or more text strings that describe the function. These strings can be used, for example, to display the flyover text for a button or to set the text in a menu item.
  - One or more icons that depict the function. These icons can be used for the images in a menu control, or for composite entries in a more sophisticated user interface.
  - The enabled/disabled state of the functionality. Instead of having to separately disable the menu item and the toolbar button, the application can disable the function that implements this interface. All components which are registered as listeners for the state change then know to disable event generation for that item and to modify the display accordingly.

  This interface can be added to an existing class or used to create an adapter (typically, by subclassing `AbstractAction`). The `Action` object can then be added to multiple `Action`-aware containers and connected to `Action`-capable components. The GUI controls can then be activated or deactivated all at once by invoking the `Action` object's `setEnabled` method.

  Note that `Action` implementations tend to be more expensive in terms of storage than a typical `ActionListener`, which does not offer the benefits of centralized control of functionality and broadcast of property changes. For this reason, you should take care to only use `Action`s where their benefits are desired, and use simple `ActionListener`s elsewhere.

  ### Swing Components Supporting `Action`

  Many of Swing's components have an `Action` property. When an `Action` is set on a component, the following things happen:

  - The `Action` is added as an `ActionListener` to the component.
  - The component configures some of its properties to match the `Action`.
  - The component installs a `PropertyChangeListener` on the `Action` so that the component can change its properties to reflect changes in the `Action`'s properties.

  The following table describes the properties used by `Swing` components that support `Actions`. In the table, button refers to any `AbstractButton` subclass, which includes not only `JButton` but also classes such as `JMenuItem`. Unless otherwise stated, a `null` property value in an `Action` (or a `Action` that is `null`) results in the button's corresponding property being set to `null`.

  Component Property | Components | Action Key | Notes
  --- | --- | --- | ---
  `enabled` | All | The `isEnabled` method |
  `toolTipText` | All | `SHORT_DESCRIPTION` |
  `actionCommand` | All | `ACTION_COMMAND_KEY` |
  `mnemonic` | All buttons | `MNEMONIC_KEY` | A `null` value or `Action` results in the button's `mnemonic` property being set to `'\0'`.
  `text` | All buttons | `NAME` | If you do not want the text of the button to mirror that of the `Action`, set the property `hideActionText` to `true`. If `hideActionText` is `true`, setting the `Action` changes the text of the button to `null` and any changes to `NAME` are ignored. `hideActionText` is useful for tool bar buttons that typically only show an `Icon`. `JToolBar.add(Action)` sets the property to `true` if the `Action` has a non-`null` value for `LARGE_ICON_KEY` or `SMALL_ICON`.
  `displayedMnemonicIndex` | All buttons | `DISPLAYED_MNEMONIC_INDEX_KEY` | If the value of `DISPLAYED_MNEMONIC_INDEX_KEY` is beyond the bounds of the text, it is ignored. When `setAction` is called, if the value from the `Action` is `null`, the displayed mnemonic index is not updated. In any subsequent changes to `DISPLAYED_MNEMONIC_INDEX_KEY`, `null` is treated as -1.
  `icon` | All buttons except of `JCheckBox`, `JToggleButton` and `JRadioButton`. | either `LARGE_ICON_KEY` or `SMALL_ICON` | The `JMenuItem` subclasses only use `SMALL_ICON`. All other buttons will use `LARGE_ICON_KEY`; if the value is `null` they use `SMALL_ICON`.
  `accelerator` | All `JMenuItem` subclasses, with the exception of `JMenu`. | `ACCELERATOR_KEY` |
  `selected` | `JToggleButton`, `JCheckBox`, `JRadioButton`, `JCheckBoxMenuItem` and `JRadioButtonMenuItem` | `SELECTED_KEY` | Components that honor this property only use the value if it is `non-null`. For example, if you set an `Action` that has a `null` value for `SELECTED_KEY` on a `JToggleButton`, the `JToggleButton` will not update it's selected state in any way. Similarly, any time the `JToggleButton`'s selected state changes it will only set the value back on the `Action` if the `Action` has a `non-null` value for `SELECTED_KEY`. Components that honor this property keep their selected state in sync with this property. When the same `Action` is used with multiple components, all the components keep their selected state in sync with this property. Mutually exclusive buttons, such as `JToggleButton`s in a `ButtonGroup`, force only one of the buttons to be selected. As such, do not use the same `Action` that defines a value for the `SELECTED_KEY` property with multiple mutually exclusive buttons.

  `JPopupMenu`, `JToolBar` and `JMenu` all provide convenience methods for creating a component and setting the `Action` on the corresponding component. Refer to each of these classes for more information.

  `Action` uses `PropertyChangeListener` to inform listeners the `Action` has changed. The beans specification indicates that a `null` property name can be used to indicate multiple values have changed. By default Swing components that take an `Action` do not handle such a change. To indicate that Swing should treat `null` according to the beans specification set the system property `swing.actions.reconfigureOnNull` to the `String` value `true`.

  See Also:
    `AbstractAction`

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static String` | `ACCELERATOR_KEY` The key used for storing a `KeyStroke` to be used as the accelerator for the action.
    `static String` | `ACTION_COMMAND_KEY` The key used to determine the command `String` for the `ActionEvent` that will be created when an `Action` is going to be notified as the result of residing in a `Keymap` associated with a `JComponent`.
    `static String` | `DEFAULT` Not currently used.
    `static String` | `DISPLAYED_MNEMONIC_INDEX_KEY` The key used for storing an `Integer` that corresponds to the index in the text (identified by the `NAME` property) that the decoration for a mnemonic should be rendered at.
    `static String` | `LARGE_ICON_KEY` The key used for storing an `Icon`.
    `static String` | `LONG_DESCRIPTION` The key used for storing a longer `String` description for the action, could be used for context-sensitive help.
    `static String` | `MNEMONIC_KEY` The key used for storing an `Integer` that corresponds to one of the `KeyEvent` key codes.
    `static String` | `NAME` The key used for storing the `String` name for the action, used for a menu or button.
    `static String` | `SELECTED_KEY` The key used for storing a `Boolean` that corresponds to the selected state.
    `static String` | `SHORT_DESCRIPTION` The key used for storing a short `String` description for the action, used for tooltip text.
    `static String` | `SMALL_ICON` The key used for storing a small `Icon`, such as `ImageIcon`.

  - ### Method Summary

    All Methods Instance Methods Abstract Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `addPropertyChangeListener(PropertyChangeListener listener)` Adds a `PropertyChange` listener.
    `Object` | `getValue(String key)` Gets one of this object's properties using the associated key.
    `boolean` | `isEnabled()` Returns the enabled state of the `Action`.
    `void` | `putValue(String key, Object value)` Sets one of this object's properties using the associated key.
    `void` | `removePropertyChangeListener(PropertyChangeListener listener)` Removes a `PropertyChange` listener.
    `void` | `setEnabled(boolean b)` Sets the enabled state of the `Action`.

    - ### Methods inherited from interface java.awt.event.ActionListener

      `actionPerformed`

- - ### Field Detail

    - #### DEFAULT

          static final String DEFAULT

      Not currently used.
      See Also:
        Constant Field Values

    - #### NAME

          static final String NAME

      The key used for storing the `String` name for the action, used for a menu or button.
      See Also:
        Constant Field Values

    - #### SHORT_DESCRIPTION

          static final String SHORT_DESCRIPTION

      The key used for storing a short `String` description for the action, used for tooltip text.
      See Also:
        Constant Field Values

    - #### LONG_DESCRIPTION

          static final String LONG_DESCRIPTION

      The key used for storing a longer `String` description for the action, could be used for context-sensitive help.
      See Also:
        Constant Field Values

    - #### SMALL_ICON

          static final String SMALL_ICON

      The key used for storing a small `Icon`, such as `ImageIcon`. This is typically used with menus such as `JMenuItem`.

      If the same `Action` is used with menus and buttons you'll typically specify both a `SMALL_ICON` and a `LARGE_ICON_KEY`. The menu will use the `SMALL_ICON` and the button will use the `LARGE_ICON_KEY`.

      See Also:
        Constant Field Values

    - #### ACTION_COMMAND_KEY

          static final String ACTION_COMMAND_KEY

      The key used to determine the command `String` for the `ActionEvent` that will be created when an `Action` is going to be notified as the result of residing in a `Keymap` associated with a `JComponent`.
      See Also:
        Constant Field Values

    - #### ACCELERATOR_KEY

          static final String ACCELERATOR_KEY

      The key used for storing a `KeyStroke` to be used as the accelerator for the action.
      Since:
        1.3
      See Also:
        Constant Field Values

    - #### MNEMONIC_KEY

          static final String MNEMONIC_KEY

      The key used for storing an `Integer` that corresponds to one of the `KeyEvent` key codes. The value is commonly used to specify a mnemonic. For example: `myAction.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_A)` sets the mnemonic of `myAction` to 'a', while `myAction.putValue(Action.MNEMONIC_KEY, KeyEvent.getExtendedKeyCodeForChar('?'))` sets the mnemonic of `myAction` to Cyrillic letter "Ef".
      Since:
        1.3
      See Also:
        Constant Field Values

    - #### SELECTED_KEY

          static final String SELECTED_KEY

      The key used for storing a `Boolean` that corresponds to the selected state. This is typically used only for components that have a meaningful selection state. For example, `JRadioButton` and `JCheckBox` make use of this but instances of `JMenu` don't.

      This property differs from the others in that it is both read by the component and set by the component. For example, if an `Action` is attached to a `JCheckBox` the selected state of the `JCheckBox` will be set from that of the `Action`. If the user clicks on the `JCheckBox` the selected state of the `JCheckBox` and the `Action` will both be updated.

      Note: the value of this field is prefixed with 'Swing' to avoid possible collisions with existing `Actions`.

      Since:
        1.6
      See Also:
        Constant Field Values

    - #### DISPLAYED_MNEMONIC_INDEX_KEY

          static final String DISPLAYED_MNEMONIC_INDEX_KEY

      The key used for storing an `Integer` that corresponds to the index in the text (identified by the `NAME` property) that the decoration for a mnemonic should be rendered at. If the value of this property is greater than or equal to the length of the text, it will treated as -1.

      Note: the value of this field is prefixed with 'Swing' to avoid possible collisions with existing `Actions`.

      Since:
        1.6
      See Also:
        `AbstractButton.setDisplayedMnemonicIndex(int)`, Constant Field Values

    - #### LARGE_ICON_KEY

          static final String LARGE_ICON_KEY

      The key used for storing an `Icon`. This is typically used by buttons, such as `JButton` and `JToggleButton`.

      If the same `Action` is used with menus and buttons you'll typically specify both a `SMALL_ICON` and a `LARGE_ICON_KEY`. The menu will use the `SMALL_ICON` and the button the `LARGE_ICON_KEY`.

      Note: the value of this field is prefixed with 'Swing' to avoid possible collisions with existing `Actions`.

      Since:
        1.6
      See Also:
        Constant Field Values

  - ### Method Detail

    - #### getValue

          Object getValue(String key)

      Gets one of this object's properties using the associated key.
      See Also:
        `putValue(java.lang.String, java.lang.Object)`

    - #### putValue

          void putValue(String key,
                        Object value)

      Sets one of this object's properties using the associated key. If the value has changed, a `PropertyChangeEvent` is sent to listeners.
      Parameters:
        `key` - a `String` containing the key
        `value` - an `Object` value

    - #### setEnabled

          void setEnabled(boolean b)

      Sets the enabled state of the `Action`. When enabled, any component associated with this object is active and able to fire this object's `actionPerformed` method. If the value has changed, a `PropertyChangeEvent` is sent to listeners.
      Parameters:
        `b` - true to enable this `Action`, false to disable it

    - #### isEnabled

          boolean isEnabled()

      Returns the enabled state of the `Action`. When enabled, any component associated with this object is active and able to fire this object's `actionPerformed` method.
      Returns:
        true if this `Action` is enabled

    - #### addPropertyChangeListener

          void addPropertyChangeListener(PropertyChangeListener listener)

      Adds a `PropertyChange` listener. Containers and attached components use these methods to register interest in this `Action` object. When its enabled state or other property changes, the registered listeners are informed of the change.
      Parameters:
        `listener` - a `PropertyChangeListener` object

    - #### removePropertyChangeListener

          void removePropertyChangeListener(PropertyChangeListener listener)

      Removes a `PropertyChange` listener.
      Parameters:
        `listener` - a `PropertyChangeListener` object
      See Also:
        `addPropertyChangeListener(java.beans.PropertyChangeListener)`

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