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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 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
.
Author: Georges Saab See Also:
/**
* 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 name="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 border="1" cellpadding="1" cellspacing="0"
* summary="Supported Action properties">
* <tr valign="top" align="left">
* <th style="background-color:#CCCCFF" align="left">Component Property
* <th style="background-color:#CCCCFF" align="left">Components
* <th style="background-color:#CCCCFF" align="left">Action Key
* <th style="background-color:#CCCCFF" align="left">Notes
* <tr valign="top" align="left">
* <td><b><code>enabled</code></b>
* <td>All
* <td>The <code>isEnabled</code> method
* <td>
* <tr valign="top" align="left">
* <td><b><code>toolTipText</code></b>
* <td>All
* <td><code>SHORT_DESCRIPTION</code>
* <td>
* <tr valign="top" align="left">
* <td><b><code>actionCommand</code></b>
* <td>All
* <td><code>ACTION_COMMAND_KEY</code>
* <td>
* <tr valign="top" align="left">
* <td><b><code>mnemonic</code></b>
* <td>All buttons
* <td><code>MNEMONIC_KEY</code>
* <td>A <code>null</code> value or <code>Action</code> results in the
* button's <code>mnemonic</code> property being set to
* <code>'\0'</code>.
* <tr valign="top" align="left">
* <td><b><code>text</code></b>
* <td>All buttons
* <td><code>NAME</code>
* <td>If you do not want the text of the button to mirror that
* of the <code>Action</code>, set the property
* <code>hideActionText</code> to <code>true</code>. If
* <code>hideActionText</code> is <code>true</code>, setting the
* <code>Action</code> changes the text of the button to
* <code>null</code> and any changes to <code>NAME</code>
* are ignored. <code>hideActionText</code> is useful for
* tool bar buttons that typically only show an <code>Icon</code>.
* <code>JToolBar.add(Action)</code> sets the property to
* <code>true</code> if the <code>Action</code> has a
* non-<code>null</code> value for <code>LARGE_ICON_KEY</code> or
* <code>SMALL_ICON</code>.
* <tr valign="top" align="left">
* <td><b><code>displayedMnemonicIndex</code></b>
* <td>All buttons
* <td><code>DISPLAYED_MNEMONIC_INDEX_KEY</code>
* <td>If the value of <code>DISPLAYED_MNEMONIC_INDEX_KEY</code> is
* beyond the bounds of the text, it is ignored. When
* <code>setAction</code> is called, if the value from the
* <code>Action</code> is <code>null</code>, the displayed
* mnemonic index is not updated. In any subsequent changes to
* <code>DISPLAYED_MNEMONIC_INDEX_KEY</code>, <code>null</code>
* is treated as -1.
* <tr valign="top" align="left">
* <td><b><code>icon</code></b>
* <td>All buttons except of <code>JCheckBox</code>,
* <code>JToggleButton</code> and <code>JRadioButton</code>.
* <td>either <code>LARGE_ICON_KEY</code> or
* <code>SMALL_ICON</code>
* <td>The <code>JMenuItem</code> subclasses only use
* <code>SMALL_ICON</code>. All other buttons will use
* <code>LARGE_ICON_KEY</code>; if the value is <code>null</code> they
* use <code>SMALL_ICON</code>.
* <tr valign="top" align="left">
* <td><b><code>accelerator</code></b>
* <td>All <code>JMenuItem</code> subclasses, with the exception of
* <code>JMenu</code>.
* <td><code>ACCELERATOR_KEY</code>
* <td>
* <tr valign="top" align="left">
* <td><b><code>selected</code></b>
* <td><code>JToggleButton</code>, <code>JCheckBox</code>,
* <code>JRadioButton</code>, <code>JCheckBoxMenuItem</code> and
* <code>JRadioButtonMenuItem</code>
* <td><code>SELECTED_KEY</code>
* <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.
* </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
*/
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.
See Also: - putValue
/**
* Gets one of this object's properties
* using the associated key.
* @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
/**
* Sets the enabled state of the <code>Action</code>. When enabled,
* any component associated with this object is active and
* able to fire this object's <code>actionPerformed</code> method.
* If the value has changed, a <code>PropertyChangeEvent</code> is sent
* to listeners.
*
* @param b true to enable this <code>Action</code>, false to disable it
*/
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.
Returns: true if this Action
is enabled
/**
* Returns the enabled state of the <code>Action</code>. When enabled,
* any component associated with this object is active and
* able to fire this object's <code>actionPerformed</code> method.
*
* @return true if this <code>Action</code> is enabled
*/
public boolean 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);
}