Author(s)Timothy Prinzing, Igor Kushnirskiy (printing support)
JTextComponent is the base class for swing text
components. It tries to be compatible with the
java.awt.TextComponent class
where it can reasonably do so. Also provided are other services
for additional flexibility (beyond the pluggable UI and bean
support).
You can find information on how to use the functionality
this class provides in
General Rules for Using Text Components,
a section in The Java Tutorial.
Caret Changes
The caret is a pluggable object in swing text components.
Notification of changes to the caret position and the selection
are sent to implementations of the CaretListener
interface that have been registered with the text component.
The UI will install a default caret unless a customized caret
has been set.
By default the caret tracks all the document changes
performed on the Event Dispatching Thread and updates it's position
accordingly if an insertion occurs before or at the caret position
or a removal occurs before the caret position. DefaultCaret
tries to make itself visible which may lead to scrolling
of a text component within JScrollPane. The default caret
behavior can be changed by the setUpdatePolicy(int) method.
Note: Non-editable text components also have a caret though
it may not be painted.
Commands
Text components provide a number of commands that can be used
to manipulate the component. This is essentially the way that
the component expresses its capabilities. These are expressed
in terms of the swing Action interface,
using the TextAction implementation.
The set of commands supported by the text component can be
found with the getActions() method. These actions
can be bound to key events, fired from buttons, etc.
Text Input
The text components support flexible and internationalized text input, using
keymaps and the input method framework, while maintaining compatibility with
the AWT listener model.
A Keymap lets an application bind key
strokes to actions.
In order to allow keymaps to be shared across multiple text components, they
can use actions that extend TextAction.
TextAction can determine which JTextComponent
most recently has or had focus and therefore is the subject of
the action (In the case that the ActionEvent
sent to the action doesn't contain the target text component as its source).
The input method framework
lets text components interact with input methods, separate software
components that preprocess events to let users enter thousands of
different characters using keyboards with far fewer keys.
JTextComponent is an active client of
the framework, so it implements the preferred user interface for interacting
with input methods. As a consequence, some key events do not reach the text
component because they are handled by an input method, and some text input
reaches the text component as committed text within an InputMethodEvent instead of as a key event.
The complete text input is the combination of the characters in
keyTyped key events and committed text in input method events.
The AWT listener model lets applications attach event listeners to
components in order to bind events to actions. Swing encourages the
use of keymaps instead of listeners, but maintains compatibility
with listeners by giving the listeners a chance to steal an event
by consuming it.
Keyboard event and input method events are handled in the following stages,
with each stage capable of consuming the event:
Stage
KeyEvent
InputMethodEvent
1.
input methods
(generated here)
2.
focus manager
3.
registered key listeners
registered input method listeners
4.
input method handling in JTextComponent
5.
keymap handling using the current keymap
6.
keyboard handling in JComponent (e.g. accelerators, component navigation, etc.)
To maintain compatibility with applications that listen to key
events but are not aware of input method events, the input
method handling in stage 4 provides a compatibility mode for
components that do not process input method events. For these
components, the committed text is converted to keyTyped key events
and processed in the key event pipeline starting at stage 3
instead of in the input method event pipeline.
By default the component will create a keymap (named DEFAULT_KEYMAP)
that is shared by all JTextComponent instances as the default keymap.
Typically a look-and-feel implementation will install a different keymap
that resolves to the default keymap for those bindings not found in the
different keymap. The minimal bindings include:
inserting content into the editor for the
printable keys.
removing content with the backspace and del
keys.
caret movement forward and backward
Model/View Split
The text components have a model-view split. A text component pulls
together the objects used to represent the model, view, and controller.
The text document model may be shared by other views which act as observers
of the model (e.g. a document may be shared by multiple components).
The model is defined by the Document interface.
This is intended to provide a flexible text storage mechanism
that tracks change during edits and can be extended to more sophisticated
models. The model interfaces are meant to capture the capabilities of
expression given by SGML, a system used to express a wide variety of
content.
Each modification to the document causes notification of the
details of the change to be sent to all observers in the form of a
DocumentEvent which allows the views to stay up to date with the model.
This event is sent to observers that have implemented the
DocumentListener
interface and registered interest with the model being observed.
Location Information
The capability of determining the location of text in
the view is provided. There are two methods, modelToView(int)
and viewToModel(Point) for determining this information.
Undo/Redo support
Support for an edit history mechanism is provided to allow
undo/redo operations. The text component does not itself
provide the history buffer by default, but does provide
the UndoableEdit records that can be used in conjunction
with a history buffer to provide the undo/redo support.
The support is provided by the Document model, which allows
one to attach UndoableEditListener implementations.
Thread Safety
The swing text components provide some support of thread
safe operations. Because of the high level of configurability
of the text components, it is possible to circumvent the
protection provided. The protection primarily comes from
the model, so the documentation of AbstractDocument
describes the assumptions of the protection provided.
The methods that are safe to call asynchronously are marked
with comments.
Newlines
For a discussion on how newlines are handled, see
DefaultEditorKit.
Warning:
Serialized objects of this class will not be compatible with
future Swing releases. The current serialization support is
appropriate for short term storage or RMI between applications running
the same version of Swing. As of 1.4, support for long term storage
of all JavaBeansTM
has been added to the java.beans package.
Please see XMLEncoder .
JTextComponentis the base class for swing text components. It tries to be compatible with thejava.awt.TextComponentclass where it can reasonably do so. Also provided are other services for additional flexibility (beyond the pluggable UI and bean support). You can find information on how to use the functionality this class provides in General Rules for Using Text Components, a section in The Java Tutorial.CaretListenerinterface that have been registered with the text component. The UI will install a default caret unless a customized caret has been set.By default the caret tracks all the document changes performed on the Event Dispatching Thread and updates it's position accordingly if an insertion occurs before or at the caret position or a removal occurs before the caret position.
DefaultCarettries to make itself visible which may lead to scrolling of a text component withinJScrollPane. The default caret behavior can be changed by the setUpdatePolicy(int) method.Note: Non-editable text components also have a caret though it may not be painted.
Actioninterface, using theTextActionimplementation. The set of commands supported by the text component can be found with the getActions() method. These actions can be bound to key events, fired from buttons, etc.A Keymap lets an application bind key strokes to actions. In order to allow keymaps to be shared across multiple text components, they can use actions that extend
TextAction.TextActioncan determine whichJTextComponentmost recently has or had focus and therefore is the subject of the action (In the case that theActionEventsent to the action doesn't contain the target text component as its source).The input method framework lets text components interact with input methods, separate software components that preprocess events to let users enter thousands of different characters using keyboards with far fewer keys.
JTextComponentis an active client of the framework, so it implements the preferred user interface for interacting with input methods. As a consequence, some key events do not reach the text component because they are handled by an input method, and some text input reaches the text component as committed text within an InputMethodEvent instead of as a key event. The complete text input is the combination of the characters inkeyTypedkey events and committed text in input method events.The AWT listener model lets applications attach event listeners to components in order to bind events to actions. Swing encourages the use of keymaps instead of listeners, but maintains compatibility with listeners by giving the listeners a chance to steal an event by consuming it.
Keyboard event and input method events are handled in the following stages, with each stage capable of consuming the event:
Stage
KeyEvent
InputMethodEvent
To maintain compatibility with applications that listen to key events but are not aware of input method events, the input method handling in stage 4 provides a compatibility mode for components that do not process input method events. For these components, the committed text is converted to keyTyped key events and processed in the key event pipeline starting at stage 3 instead of in the input method event pipeline.
By default the component will create a keymap (named DEFAULT_KEYMAP) that is shared by all JTextComponent instances as the default keymap. Typically a look-and-feel implementation will install a different keymap that resolves to the default keymap for those bindings not found in the different keymap. The minimal bindings include:
The model is defined by the Document interface. This is intended to provide a flexible text storage mechanism that tracks change during edits and can be extended to more sophisticated models. The model interfaces are meant to capture the capabilities of expression given by SGML, a system used to express a wide variety of content. Each modification to the document causes notification of the details of the change to be sent to all observers in the form of a DocumentEvent which allows the views to stay up to date with the model. This event is sent to observers that have implemented the DocumentListener interface and registered interest with the model being observed.
UndoableEditrecords that can be used in conjunction with a history buffer to provide the undo/redo support. The support is provided by the Document model, which allows one to attach UndoableEditListener implementations.AbstractDocumentdescribes the assumptions of the protection provided. The methods that are safe to call asynchronously are marked with comments.Warning: Serialized objects of this class will not be compatible with future Swing releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Swing. As of 1.4, support for long term storage of all JavaBeansTM has been added to the
java.beanspackage. Please see XMLEncoder .