src/java.desktop/share/classes/javax/swing/Action.java

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package javax.swing;

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

/**
 * 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>
 *
 * <h2><a id="buttonActions"></a>Swing Components Supporting <code>Action</code></h2>
 * <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.
     */
    public static final String DEFAULT = "Default";
    /**
     * 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 <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 <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 <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 <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 <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 <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('ф'))</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 <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 <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 <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.
     *
     * @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 <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 {@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 {@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 {@code sender} can be {@code null}.
     * The method must return false if the action is disabled.
     *
     * @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 <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 <code>PropertyChange</code> listener.
     *
     * @param listener  a <code>PropertyChangeListener</code> object
     * @see #addPropertyChangeListener
     */
    public void removePropertyChangeListener(PropertyChangeListener listener);

}