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package javax.swing;

import java.awt.*;
import java.awt.event.*;
import java.beans.*;


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 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 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.


Supported Action properties

 

   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 JToggleButtons 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.

Author:Georges Saab
See Also:
Since:1.2
/**
 * The <code>Action</code> interface provides a useful extension to the
 * <code>ActionListener</code>
 * interface in cases where the same functionality may be accessed by
 * several controls.
 * <p>
 * In addition to the <code>actionPerformed</code> method defined by the
 * <code>ActionListener</code> interface, this interface allows the
 * application to define, in a single place:
 * <ul>
 * <li>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.
 * <li>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.
 * <li>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.
 * </ul>
 * <p>
 * This interface can be added to an existing class or used to create an
 * adapter (typically, by subclassing <code>AbstractAction</code>).
 * The <code>Action</code> object
 * can then be added to multiple <code>Action</code>-aware containers
 * and connected to <code>Action</code>-capable
 * components. The GUI controls can then be activated or
 * deactivated all at once by invoking the <code>Action</code> object's
 * <code>setEnabled</code> method.
 * <p>
 * Note that <code>Action</code> implementations tend to be more expensive
 * in terms of storage than a typical <code>ActionListener</code>,
 * 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 <code>Action</code>s where their benefits
 * are desired, and use simple <code>ActionListener</code>s elsewhere.
 * <br>
 *
 * <h3><a id="buttonActions"></a>Swing Components Supporting <code>Action</code></h3>
 * <p>
 * Many of Swing's components have an <code>Action</code> property.  When
 * an <code>Action</code> is set on a component, the following things
 * happen:
 * <ul>
 * <li>The <code>Action</code> is added as an <code>ActionListener</code> to
 *     the component.
 * <li>The component configures some of its properties to match the
 *      <code>Action</code>.
 * <li>The component installs a <code>PropertyChangeListener</code> on the
 *     <code>Action</code> so that the component can change its properties
 *     to reflect changes in the <code>Action</code>'s properties.
 * </ul>
 * <p>
 * The following table describes the properties used by
 * <code>Swing</code> components that support <code>Actions</code>.
 * In the table, <em>button</em> refers to any
 * <code>AbstractButton</code> subclass, which includes not only
 * <code>JButton</code> but also classes such as
 * <code>JMenuItem</code>. Unless otherwise stated, a
 * <code>null</code> property value in an <code>Action</code> (or a
 * <code>Action</code> that is <code>null</code>) results in the
 * button's corresponding property being set to <code>null</code>.
 *
 * <table class="striped">
 * <caption>Supported Action properties</caption>
 * <thead>
 *  <tr>
 *    <th scope="col">Component Property
 *    <th scope="col">Components
 *    <th scope="col">Action Key
 *    <th scope="col">Notes
 * </thead>
 * <tbody>
 *  <tr>
 *    <th scope="row">{@code enabled}
 *    <td>All
 *    <td>The {@code isEnabled} method
 *    <td>&nbsp;
 *  <tr>
 *    <th scope="row">{@code toolTipText}
 *    <td>All
 *    <td>{@code SHORT_DESCRIPTION}
 *    <td>&nbsp;
 *  <tr>
 *    <th scope="row">{@code actionCommand}
 *    <td>All
 *    <td>{@code ACTION_COMMAND_KEY}
 *    <td>&nbsp;
 *  <tr>
 *    <th scope="row">{@code mnemonic}
 *    <td>All buttons
 *    <td>{@code MNEMONIC_KEY}
 *    <td>A {@code null} value or {@code Action} results in the button's
 *    {@code mnemonic} property being set to {@code '\0'}.
 *  <tr>
 *    <th scope="row">{@code text}
 *    <td>All buttons
 *    <td>{@code NAME}
 *    <td>If you do not want the text of the button to mirror that of the
 *    {@code Action}, set the property {@code hideActionText} to {@code true}.
 *    If {@code hideActionText} is {@code true}, setting the {@code Action}
 *    changes the text of the button to {@code null} and any changes to
 *    {@code NAME} are ignored. {@code hideActionText} is useful for tool bar
 *    buttons that typically only show an {@code Icon}.
 *    {@code JToolBar.add(Action)} sets the property to {@code true} if the
 *    {@code Action} has a non-{@code null} value for {@code LARGE_ICON_KEY} or
 *    {@code SMALL_ICON}.
 *  <tr>
 *    <th scope="row">{@code displayedMnemonicIndex}
 *    <td>All buttons
 *    <td>{@code DISPLAYED_MNEMONIC_INDEX_KEY}
 *    <td>If the value of {@code DISPLAYED_MNEMONIC_INDEX_KEY} is beyond the
 *    bounds of the text, it is ignored. When {@code setAction} is called, if
 *    the value from the {@code Action} is {@code null}, the displayed mnemonic
 *    index is not updated. In any subsequent changes to
 *    {@code DISPLAYED_MNEMONIC_INDEX_KEY}, {@code null} is treated as -1.
 *  <tr>
 *    <th scope="row">{@code icon}
 *    <td>All buttons except of {@code JCheckBox}, {@code JToggleButton} and
 *    {@code JRadioButton}.
 *    <td>either {@code LARGE_ICON_KEY} or {@code SMALL_ICON}
 *    <td>The {@code JMenuItem} subclasses only use {@code SMALL_ICON}. All
 *    other buttons will use {@code LARGE_ICON_KEY}; if the value is
 *    {@code null} they use {@code SMALL_ICON}.
 *  <tr>
 *    <th scope="row">{@code accelerator}
 *    <td>All {@code JMenuItem} subclasses, with the exception of {@code JMenu}.
 *    <td>{@code ACCELERATOR_KEY}
 *    <td>&nbsp;
 *  <tr>
 *    <th scope="row">{@code selected}
 *    <td>{@code JToggleButton}, {@code JCheckBox}, {@code JRadioButton},
 *    {@code JCheckBoxMenuItem} and {@code JRadioButtonMenuItem}
 *    <td>{@code SELECTED_KEY}
 *    <td>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}.
 *    <br>
 *    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.
 * </tbody>
 * </table>
 * <p>
 * <code>JPopupMenu</code>, <code>JToolBar</code> and <code>JMenu</code>
 * all provide convenience methods for creating a component and setting the
 * <code>Action</code> on the corresponding component.  Refer to each of
 * these classes for more information.
 * <p>
 * <code>Action</code> uses <code>PropertyChangeListener</code> to
 * inform listeners the <code>Action</code> has changed.  The beans
 * specification indicates that a <code>null</code> property name can
 * be used to indicate multiple values have changed.  By default Swing
 * components that take an <code>Action</code> do not handle such a
 * change.  To indicate that Swing should treat <code>null</code>
 * according to the beans specification set the system property
 * <code>swing.actions.reconfigureOnNull</code> to the <code>String</code>
 * value <code>true</code>.
 *
 * @author Georges Saab
 * @see AbstractAction
 * @since 1.2
 */
public interface Action extends ActionListener {
    /**
     * Useful constants that can be used as the storage-retrieval key
     * when setting or getting one of this object's properties (text
     * or icon).
     */
    
Not currently used.

/**
     * Not currently used.
     */
    public static final String DEFAULT = "Default";
    
The key used for storing the String name
for the action, used for a menu or button.

/**
     * The key used for storing the <code>String</code> name
     * for the action, used for a menu or button.
     */
    public static final String NAME = "Name";
    
The key used for storing a short String
description for the action, used for tooltip text.

/**
     * The key used for storing a short <code>String</code>
     * description for the action, used for tooltip text.
     */
    public static final String SHORT_DESCRIPTION = "ShortDescription";
    
The key used for storing a longer String
description for the action, could be used for context-sensitive help.

/**
     * The key used for storing a longer <code>String</code>
     * description for the action, could be used for context-sensitive help.
     */
    public static final String LONG_DESCRIPTION = "LongDescription";
    
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.

/**
     * The key used for storing a small <code>Icon</code>, such
     * as <code>ImageIcon</code>.  This is typically used with
     * menus such as <code>JMenuItem</code>.
     * <p>
     * If the same <code>Action</code> is used with menus and buttons you'll
     * typically specify both a <code>SMALL_ICON</code> and a
     * <code>LARGE_ICON_KEY</code>.  The menu will use the
     * <code>SMALL_ICON</code> and the button will use the
     * <code>LARGE_ICON_KEY</code>.
     */
    public static final String SMALL_ICON = "SmallIcon";

    
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.

/**
     * The key used to determine the command <code>String</code> for the
     * <code>ActionEvent</code> that will be created when an
     * <code>Action</code> is going to be notified as the result of
     * residing in a <code>Keymap</code> associated with a
     * <code>JComponent</code>.
     */
    public static final String ACTION_COMMAND_KEY = "ActionCommandKey";

    
The key used for storing a KeyStroke to be used as the
accelerator for the action.

Since:1.3
/**
     * The key used for storing a <code>KeyStroke</code> to be used as the
     * accelerator for the action.
     *
     * @since 1.3
     */
    public static final String ACCELERATOR_KEY="AcceleratorKey";

    
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
/**
     * The key used for storing an <code>Integer</code> that corresponds to
     * one of the <code>KeyEvent</code> key codes.  The value is
     * commonly used to specify a mnemonic.  For example:
     * <code>myAction.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_A)</code>
     * sets the mnemonic of <code>myAction</code> to 'a', while
     * <code>myAction.putValue(Action.MNEMONIC_KEY, KeyEvent.getExtendedKeyCodeForChar('\u0444'))</code>
     * sets the mnemonic of <code>myAction</code> to Cyrillic letter "Ef".
     *
     * @since 1.3
     */
    public static final String MNEMONIC_KEY="MnemonicKey";

    
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
/**
     * The key used for storing a <code>Boolean</code> that corresponds
     * to the selected state.  This is typically used only for components
     * that have a meaningful selection state.  For example,
     * <code>JRadioButton</code> and <code>JCheckBox</code> make use of
     * this but instances of <code>JMenu</code> don't.
     * <p>
     * This property differs from the others in that it is both read
     * by the component and set by the component.  For example,
     * if an <code>Action</code> is attached to a <code>JCheckBox</code>
     * the selected state of the <code>JCheckBox</code> will be set from
     * that of the <code>Action</code>.  If the user clicks on the
     * <code>JCheckBox</code> the selected state of the <code>JCheckBox</code>
     * <b>and</b> the <code>Action</code> will <b>both</b> be updated.
     * <p>
     * Note: the value of this field is prefixed with 'Swing' to
     * avoid possible collisions with existing <code>Actions</code>.
     *
     * @since 1.6
     */
    public static final String SELECTED_KEY = "SwingSelectedKey";

    
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.

See Also:
  • setDisplayedMnemonicIndex.setDisplayedMnemonicIndex
Since:1.6
/**
     * The key used for storing an <code>Integer</code> that corresponds
     * to the index in the text (identified by the <code>NAME</code>
     * 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.
     * <p>
     * Note: the value of this field is prefixed with 'Swing' to
     * avoid possible collisions with existing <code>Actions</code>.
     *
     * @see AbstractButton#setDisplayedMnemonicIndex
     * @since 1.6
     */
    public static final String DISPLAYED_MNEMONIC_INDEX_KEY =
                                 "SwingDisplayedMnemonicIndexKey";

    
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
/**
     * The key used for storing an <code>Icon</code>.  This is typically
     * used by buttons, such as <code>JButton</code> and
     * <code>JToggleButton</code>.
     * <p>
     * If the same <code>Action</code> is used with menus and buttons you'll
     * typically specify both a <code>SMALL_ICON</code> and a
     * <code>LARGE_ICON_KEY</code>.  The menu will use the
     * <code>SMALL_ICON</code> and the button the <code>LARGE_ICON_KEY</code>.
     * <p>
     * Note: the value of this field is prefixed with 'Swing' to
     * avoid possible collisions with existing <code>Actions</code>.
     *
     * @since 1.6
     */
    public static final String LARGE_ICON_KEY = "SwingLargeIconKey";

    
Gets one of this object's properties
using the associated key.

Params:
  • key – a String containing the key
See Also:
Returns:the Object value
/**
     * Gets one of this object's properties
     * using the associated key.
     *
     * @param key a {@code String} containing the key
     * @return the {@code Object} value
     * @see #putValue
     */
    public Object getValue(String key);
    
Sets one of this object's properties
using the associated key. If the value has
changed, a PropertyChangeEvent is sent
to listeners.

Params:
  • key –    a String containing the key
  • value –  an Object value
/**
     * Sets one of this object's properties
     * using the associated key. If the value has
     * changed, a <code>PropertyChangeEvent</code> is sent
     * to listeners.
     *
     * @param key    a <code>String</code> containing the key
     * @param value  an <code>Object</code> value
     */
    public void putValue(String key, Object value);

    
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. 
Params:
  • b – true to enable this Action, false to disable it
See Also:
/**
     * Sets the enabled state of the {@code Action}.  When enabled,
     * any component associated with this object is active and
     * able to fire this object's {@code actionPerformed} method.
     * If the value has changed, a {@code PropertyChangeEvent} is sent
     * to listeners.
     *
     * @param  b true to enable this {@code Action}, false to disable it
     * @see #accept
     */
    public void setEnabled(boolean b);
    
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. 
See Also:
Returns:true if this Action is enabled
/**
     * Returns the enabled state of the {@code Action}. When enabled,
     * any component associated with this object is active and
     * able to fire this object's {@code actionPerformed} method.
     *
     * @return true if this {@code Action} is enabled
     * @see #accept
     */
    public boolean isEnabled();

    
Determines whether the action should be performed with the specified sender object. The sender can be null. The method must return false if the action is disabled. 


Params:
  • sender – the object to check, can be null
See Also:
Returns:true if the action should be performed with the sender object, must be false if the action is disabled.
/**
     * Determines whether the action should be performed with the specified
     * sender object. The {@code sender} can be {@code null}.
     * The method must return false if the action is disabled.
     * <p>
     * @param sender the object to check, can be null
     * @return {@code true} if the action should be performed with the sender
     *         object, must be false if the action is disabled.
     * @see #isEnabled
     * @see #setEnabled
     */
    default boolean accept(Object sender) {
        return isEnabled();
    }

    
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.

Params:
  • listener –  a PropertyChangeListener object
/**
     * Adds a <code>PropertyChange</code> listener. Containers and attached
     * components use these methods to register interest in this
     * <code>Action</code> object. When its enabled state or other property
     * changes, the registered listeners are informed of the change.
     *
     * @param listener  a <code>PropertyChangeListener</code> object
     */
    public void addPropertyChangeListener(PropertyChangeListener listener);
    
Removes a PropertyChange listener.

Params:
  • listener –  a PropertyChangeListener object
See Also:
/**
     * Removes a <code>PropertyChange</code> listener.
     *
     * @param listener  a <code>PropertyChangeListener</code> object
     * @see #addPropertyChangeListener
     */
    public void removePropertyChangeListener(PropertyChangeListener listener);

}