Handling Events - Beginning Java - page 936

can add the very same Action object to both a menu and a toolbar, and because the Action object is its
own listener, you automatically get both the menu item and the toolbar button supported by the same action.
Clever, eh?
There's more. You can construct any type of menu item, including those of type JCheckBoxMenuItem
and JRadioButtonMenuItem , from Action objects, so if you want to have these on your menus, you can.
You just add the menu items you create from your Action objects to a menu in the way you have seen. First,
you need to look at the Action interface.
The Action Interface
In general, properties are items of information that relate to a particular object and are stored as part of the
object. Properties are often stored in a map, where a key identifies a particular property, and the value cor-
responding to that property can be stored in association with the key. The Properties class that is defined
in the java.util package does exactly that. The Action interface has provision for storing several ba-
sic standard properties that relate to an Action object. These properties are accessed through keys of type
String. The identifiers for the keys that are defined in the Action interface and the corresponding values
are the following:
• NAME : A String object that is the label for a menu item or a toolbar button.
• SMALL_ICON : A javax.Swing.Icon reference to a small icon for a menu item (typically a
javax.Swing.ImageIcon object).
• LARGE_ICON_KEY : An Icon reference to a large icon for a toolbar button (typically an ImageIcon
object).
• SHORT_DESCRIPTION : A String object that is a tooltip.
• LONG_DESCRIPTION : A String object that is a context-sensitive help message.
• ACCELERATOR_KEY : A javax.swing.KeyStroke object that represents a key combination is the
accelerator for the action.
• DISPLAYED_MNEMONIC_INDEX_KEY : An Integer object indicating where in the NAME property
value the decoration (which is an underline) for a mnemonic should be rendered. You use this to
create a visual cue to the character for the accelerator.
• MNEMONIC_KEY : An Integer that corresponds to a KeyEvent key code.
• SELECTED_KEY : A Boolean object that records the selected or unselected state.
• ACTION_COMMAND_KEY : A String object that is the command string for the action.
Just so you are aware of them I have included the complete set here, but you will only use a few of them
in Sketcher. You are not obliged to provide for all of these properties in your action classes, but the Action
interface provides the framework for it. There is another key defined in the interface with the name DEFAULT ,
but this is not used currently.
Action Methods
The Action interface also declares the following methods:
• void putValue(String key,Object value) : Stores the object value associated with the key
constant key in the action object. To store the name of an action within a class method, you might
write: