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javax.swing
public interface: Action [javadoc | source]

All Implemented Interfaces:
    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:

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 Actions where their benefits are desired, and use simple ActionListeners 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 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 {@code non-null}. For example, if you set an {@code Action} that has a {@code null} value for {@code SELECTED_KEY} on a {@code JToggleButton}, the {@code JToggleButton} will not update it's selected state in any way. Similarly, any time the {@code JToggleButton}'s selected state changes it will only set the value back on the {@code Action} if the {@code Action} has a {@code non-null} value for {@code SELECTED_KEY}.
Components that honor this property keep their selected state in sync with this property. When the same {@code Action} is used with multiple components, all the components keep their selected state in sync with this property. Mutually exclusive buttons, such as {@code JToggleButton}s in a {@code ButtonGroup}, force only one of the buttons to be selected. As such, do not use the same {@code Action} that defines a value for the {@code 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.

Field Summary
public static final  String DEFAULT    Not currently used. 
public static final  String NAME    The key used for storing the String name for the action, used for a menu or button. 
public static final  String SHORT_DESCRIPTION    The key used for storing a short String description for the action, used for tooltip text. 
public static final  String LONG_DESCRIPTION    The key used for storing a longer String description for the action, could be used for context-sensitive help. 
public 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

public 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
public static final  String ACCELERATOR_KEY    The key used for storing a KeyStroke to be used as the accelerator for the action.
    since: 1.3 -
 
public 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('\u0444')) sets the mnemonic of myAction to Cyrillic letter "Ef".
    since: 1.3 -
 
public 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 -
 
public 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.

    Also see:
    AbstractButton#setDisplayedMnemonicIndex
    since: 1.6 -
 
public 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 -
 
Method from javax.swing.Action Summary:
addPropertyChangeListener,   getValue,   isEnabled,   putValue,   removePropertyChangeListener,   setEnabled
Method from javax.swing.Action Detail:
 public  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.
 public Object getValue(String key)
    Gets one of this object's properties using the associated key.
 public 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.
 public  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.
 public  void removePropertyChangeListener(PropertyChangeListener listener)
    Removes a PropertyChange listener.
 public  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.