25.3 Other Accessible Objects

Before going further, there are several simple objects in the accessibility package used by AccessibleContext that we should discuss in more detail.

25.3.1 The AccessibleState Class

Each accessible component can have one or more states associated with it. An assistive technology can query these states at any time to determine how best to deal with the component. The accessible states can only be retrieved, however, and not set. There are two classes that the Accessible package uses to handle states: AccessibleState and AccessibleStateSet.

The AccessibleState class contains an enumeration of static objects that define states that any accessible component can have. Note that a component can be in more than one state at any time. A list of the possible states that an accessible object can be in, along with a brief description of each, is shown in Table 25-3.

Table 25-3. AccessibleState constants

State	Meaning
ACTIVE	The window, dialog, or frame is the active one.
ARMED	The object, such as a button, has been pressed but not released, and the mouse cursor is still over the button.
BUSY	The object is busy processing and should not be interrupted.
CHECKED	The object is checked.
COLLAPSED	The object, such as a node in a tree, is collapsed.
EDITABLE	The object supports any form of editing.
ENABLED	The object is enabled.
EXPANDABLE	The object, such as a node in a tree, can report its children.
EXPANDED	The object, such as a node in a tree, is expanded.
FOCUSABLE	The object can accept the focus.
FOCUSED	The object has the focus.
HORIZONTAL	The object's orientation is horizontal.
ICONFIED	The object is iconified.
MODAL	The object is modal and must be closed before the user can switch to another window.
MULTI_LINE	The object is capable of using many lines of text.
MULTISELECTABLE	The object allows multiple children to be selected at the same time.
OPAQUE	The object is completely filled (i.e., paints every pixel) and thus does not allow transparency.
PRESSED	The object, such as a button, is being pressed but has not been released.
RESIZABLE	The object is resizable.
SELECTABLE	The object is capable of being selected from its parent.
SELECTED	The object is selected.
SHOWING	The object and each of its ancestors are visible.
SINGLE_LINE	The object is capable of using only a single line of text.
TRANSIENT	The object is transient. In the context of accessibility, transient objects serve only to help other components perform some underlying duty, such as rendering to the screen. These objects do not generate change events that an assistive technology would be interested in, but are necessary to allow assistive technologies to query through the component hierarchy.
VERTICAL	The object's orientation is vertical.
VISIBLE	The object is visible.

Some of these states are specific to various objects. For example, a JButton cannot be COLLAPSED, and a JLabel cannot be EDITABLE. An assistive technology, however, should know which objects can have which states and how to act accordingly. Note that the individual states of AccessibleState are immutable objects. In order to work with a group (or set) of them, you will need the services of the AccessibleStateSet object.

25.3.1.1 Constructor

protected AccessibleState(String key)

This protected constructor is called using any of the states listed above to instantiate an AccessibleState object. It is protected to allow each of the above constants to remain as a strongly typed, static enumeration of states. Follow this procedure if you subclass AccessibleState with your own states.

25.3.2 The AccessibleStateSet Class

Because an accessible component can have more than one accessible state at the same time, you must access each of the states through the use of an AccessibleStateSet object. This object is simply a repository (or set) of accessible states, as well as various methods that search and identify particular states. You can retrieve an AccessibleStateSet for each accessible component with the getAccessibleStateSet( ) accessor of the AccessibleContext object.

25.3.2.1 Constructors

AccessibleStateSet( )

Create an empty state set.

AccessibleStateSet(AccessibleState[] states)

Create a state set using the array of AccessibleState objects passed in to initialize itself.

25.3.2.2 Methods

The methods of AccessibleStateSet give you everything you need to manipulate the set:

public boolean add(AccessibleState state)

Add a new AccessibleState to the set, returning true if successful. If the state is already present, it is not added, and the method returns false.

public void addAll(AccessibleState[] states)

Add all the states specified in the array to the set, ignoring any that are already present.

public void clear( )

Clear all states from the state set.

public boolean contains(AccessibleState state)

Return a boolean indicating whether the given state is included in the set.

public boolean remove(AccessibleState state)

Remove a specific AccessibleState from the set, returning true if successful. If the state is not present in the set, the method returns false.

public AccessibleState[] toArray( )

Return all the states in the set as an array of AccessibleState objects.

25.3.3 The AccessibleRole Class

A common way to determine the purpose or function of an accessible component is to check its accessibility role. All accessibility roles are bundled inside the AccessibleRole class, which, like the AccessibleState class, consists only of static constants. An assistive technology can query these read-only roles from AccessibleContext to better determine which type of component it is dealing with. If a desired role does not exist in this class, you can always extend the AccessibleRole class into a subclass of your own and include the newly defined role there. Because they are all of type AccessibleRole, the static constants within this class can be used in conjunction with the getAccessibleRole( ) method of an AccessibleContext object.

Table 25-4 outlines each of the accessibility roles.

Table 25-4. AccessibleRole constants

Constant	Meaning
ALERT	Provides an alert to the user
AWT_COMPONENT	A generic AWT component
CANVAS1.3	An object that you can paint on and receive events from
CHECK_BOX	A dual-state button or checkbox
COLOR_CHOOSER	An object for selecting a color
COLUMN_HEADER	A header for a column of data
COMBO_BOX	A combo box component
DATE_EDITOR1.4	An editor that can manipulate Date and Time objects
DESKTOP_ICON	An internal frame that has been iconified
DESKTOP_PANE	A desktop pane that supports internal frames
DIALOG	A top-level dialog box
DIRECTORY_PANE	A specialty pane used to locate directories on a filesystem
FILE_CHOOSER	A specialty dialog box for choosing a file
FILLER	Any object that takes up space in a user interface
FONT_CHOOSER1.4	A component for picking fonts
FRAME	A top-level frame
GLASS_PANE	The glass pane of a frame or applet
GROUP_BOX1.4	Any bordered container
HYPERLINK1.4	A link in a hypertext document
ICON1.3	An icon (small graphic image)
INTERNAL_FRAME	An internal frame inside a desktop frame
LABEL	A string-based label
LAYERED_PANE	A layered-pane object
LIST	A list object
LIST_ITEM1.3	An element in a list
MENU	A standard menu that descends from a menu bar
MENU_BAR	A menu bar object
MENU_ITEM	A menu item inside a menu
OPTION_PANE	An object that displays a pop-up message
PAGE_TAB	An page tab object, typically a descendant of a page tab list
PAGE_TAB_LIST	A grouping of page tabs
PANEL	A panel object
PASSWORD_TEXT	A password text field that masks its entry text
POPUP_MENU	A pop-up menu
PROGRESS_BAR	A progress bar object
PUSH_BUTTON	A standard button
RADIO_BUTTON	A radio button
ROOT_PANE	The root pane of a frame
ROW_HEADER	A header for a row of data
SCROLL_BAR	A scrollbar
SCROLL_PANE	A scrollpane object
SEPARATOR	A lined separator used in conjunction with a layout manager
SLIDER	A slider object
SPIN_BOX1.4	A spinner component
SPLIT_PANE	A pane that is split into two adjustable halves
STATUS_BAR1.4	A label (or labels) used to show application status information
SWING_COMPONENT	A generic Swing component
TABLE	A table object
TEXT	A generic object that displays text
TOGGLE_BUTTON	A dual-state button that does not provide a separate state
TOOL_BAR	A toolbar object
TOOL_TIP	A tooltip object
TREE	A tree object
UNKNOWN	An unknown object
VIEWPORT	A viewport used in a scrollpane
WINDOW	A top-level window without a border or title
1.3since 1.3, 1.4since 1.4

25.3.3.1 Constructor

protected AccessibleRole(String key)

This is the only constructor for the AccessibleRole class. Note that the constructor is protected; there is no public constructor for this class. The constructor takes a single String that corresponds to the locale for each of the accessible roles. This locale determines how to translate each of the states and roles into a human-readable form.