Java tutorial
/* * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ 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> * <tr> * <th scope="row">{@code toolTipText} * <td>All * <td>{@code SHORT_DESCRIPTION} * <td> * <tr> * <th scope="row">{@code actionCommand} * <td>All * <td>{@code ACTION_COMMAND_KEY} * <td> * <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> * <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('\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 <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); }