Interface Action
The Action interface provides a useful extension to the ActionListener interface in cases where the same functionality may be accessed by several controls.
- 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
- 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 .
Setenabled method in java
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
- 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 .
Field Summary
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 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.
The key used for storing a longer String description for the action, could be used for context-sensitive help.
Setenabled method in java
State model for buttons. This model is used for regular buttons, as well as check boxes and radio buttons, which are special kinds of buttons. In practice, a button’s UI takes the responsibility of calling methods on its model to manage the state, as detailed below: In simple terms, pressing and releasing the mouse over a regular button triggers the button and causes and ActionEvent to be fired. The same behavior can be produced via a keyboard key defined by the look and feel of the button (typically the SPACE BAR). Pressing and releasing this key while the button has focus will give the same results. For check boxes and radio buttons, the mouse or keyboard equivalent sequence just described causes the button to become selected. In details, the state model for buttons works as follows when used with the mouse:
Pressing the mouse on top of a button makes the model both armed and pressed. As long as the mouse remains down, the model remains pressed, even if the mouse moves outside the button. On the contrary, the model is only armed while the mouse remains pressed within the bounds of the button (it can move in or out of the button, but the model is only armed during the portion of time spent within the button). A button is triggered, and an ActionEvent is fired, when the mouse is released while the model is armed — meaning when it is released over top of the button after the mouse has previously been pressed on that button (and not already released). Upon mouse release, the model becomes unarmed and unpressed. In details, the state model for buttons works as follows when used with the keyboard:
Pressing the look and feel defined keyboard key while the button has focus makes the model both armed and pressed. As long as this key remains down, the model remains in this state. Releasing the key sets the model to unarmed and unpressed, triggers the button, and causes an ActionEvent to be fired.
Method Summary
Sets the action command string that gets sent as part of the ActionEvent when the button is triggered.
Identifies the group the button belongs to — needed for radio buttons, which are mutually exclusive within their group.