Interface Document

The Document is a container for text that serves as the model for swing text components. The goal for this interface is to scale from very simple needs (a plain text textfield) to complex needs (an HTML or XML document, for example).

Content

At the simplest level, text can be modeled as a linear sequence of characters. To support internationalization, the Swing text model uses unicode characters. The sequence of characters displayed in a text component is generally referred to as the component's content.

To refer to locations within the sequence, the coordinates used are the location between two characters. As the diagram below shows, a location in a text document can be referred to as a position, or an offset. This position is zero-based.

In the example, if the content of a document is the sequence "The quick brown fox," as shown in the preceding diagram, the location just before the word "The" is 0, and the location after the word "The" and before the whitespace that follows it is 3. The entire sequence of characters in the sequence "The" is called a range.

The following methods give access to the character data that makes up the content.

• getLength()
• getText(int, int)
• getText(int, int, javax.swing.text.Segment)

Structure

Text is rarely represented simply as featureless content. Rather, text typically has some sort of structure associated with it. Exactly what structure is modeled is up to a particular Document implementation. It might be as simple as no structure (i.e. a simple text field), or it might be something like diagram below.

The unit of structure (i.e. a node of the tree) is referred to by the Element interface. Each Element can be tagged with a set of attributes. These attributes (name/value pairs) are defined by the AttributeSet interface.

The following methods give access to the document structure.

• getDefaultRootElement()
• getRootElements()

Mutations

All documents need to be able to add and remove simple text. Typically, text is inserted and removed via gestures from a keyboard or a mouse. What effect the insertion or removal has upon the document structure is entirely up to the implementation of the document.

The following methods are related to mutation of the document content:

• insertString(int, java.lang.String, javax.swing.text.AttributeSet)
• remove(int, int)
• createPosition(int)

Notification

Mutations to the Document must be communicated to interested observers. The notification of change follows the event model guidelines that are specified for JavaBeans. In the JavaBeans event model, once an event notification is dispatched, all listeners must be notified before any further mutations occur to the source of the event. Further, order of delivery is not guaranteed.

Notification is provided as two separate events, DocumentEvent, and UndoableEditEvent. If a mutation is made to a Document through its api, a DocumentEvent will be sent to all of the registered DocumentListeners. If the Document implementation supports undo/redo capabilities, an UndoableEditEvent will be sent to all of the registered UndoableEditListeners. If an undoable edit is undone, a DocumentEvent should be fired from the Document to indicate it has changed again. In this case however, there should be no UndoableEditEvent generated since that edit is actually the source of the change rather than a mutation to the Document made through its api.

Referring to the above diagram, suppose that the component shown on the left mutates the document object represented by the blue rectangle. The document responds by dispatching a DocumentEvent to both component views and sends an UndoableEditEvent to the listening logic, which maintains a history buffer.

Now suppose that the component shown on the right mutates the same document. Again, the document dispatches a DocumentEvent to both component views and sends an UndoableEditEvent to the listening logic that is maintaining the history buffer.

If the history buffer is then rolled back (i.e. the last UndoableEdit undone), a DocumentEvent is sent to both views, causing both of them to reflect the undone mutation to the document (that is, the removal of the right component's mutation). If the history buffer again rolls back another change, another DocumentEvent is sent to both views, causing them to reflect the undone mutation to the document -- that is, the removal of the left component's mutation.

The methods related to observing mutations to the document are:

• addDocumentListener(DocumentListener)
• removeDocumentListener(DocumentListener)
• addUndoableEditListener(UndoableEditListener)
• removeUndoableEditListener(UndoableEditListener)

Properties

Document implementations will generally have some set of properties associated with them at runtime. Two well known properties are the StreamDescriptionProperty, which can be used to describe where the Document came from, and the TitleProperty, which can be used to name the Document. The methods related to the properties are:

• getProperty(java.lang.Object)
• putProperty(java.lang.Object, java.lang.Object)

For more information on the Document class, see The Swing Connection and most particularly the article, The Element Interface.

Fields

StreamDescriptionProperty

static final String StreamDescriptionProperty

The property name for the description of the stream used to initialize the document. This should be used if the document was initialized from a stream and anything is known about the stream.

See Also:

Constant Field Values

TitleProperty

static final String TitleProperty

The property name for the title of the document, if there is one.

See Also:

Constant Field Values

Methods

getLength

int getLength()

Returns number of characters of content currently in the document.

Returns:

number of characters >= 0

addDocumentListener

void addDocumentListener(DocumentListener listener)

Registers the given observer to begin receiving notifications when changes are made to the document.

Parameters:

listener - the observer to register

See Also:

removeDocumentListener(javax.swing.event.DocumentListener)

removeDocumentListener

void removeDocumentListener(DocumentListener listener)

Unregisters the given observer from the notification list so it will no longer receive change updates.

Parameters:

listener - the observer to register

See Also:

addDocumentListener(javax.swing.event.DocumentListener)

addUndoableEditListener

void addUndoableEditListener(UndoableEditListener listener)

Registers the given observer to begin receiving notifications when undoable edits are made to the document.

Parameters:

listener - the observer to register

See Also:

UndoableEditEvent

removeUndoableEditListener

void removeUndoableEditListener(UndoableEditListener listener)

Unregisters the given observer from the notification list so it will no longer receive updates.

Parameters:

listener - the observer to register

See Also:

UndoableEditEvent

getProperty

Object getProperty(Object key)

Gets the properties associated with the document.

Parameters:

key - a non-null property key

Returns:

the properties

See Also:

putProperty(Object, Object)

putProperty

void putProperty(Object key,
                 Object value)

Associates a property with the document. Two standard property keys provided are: StreamDescriptionProperty and TitleProperty. Other properties, such as author, may also be defined.

Parameters:

key - the non-null property key

value - the property value

See Also:

getProperty(Object)

remove

void remove(int offs,
            int len)
     throws BadLocationException

Parameters:

offs - the offset from the beginning >= 0

len - the number of characters to remove >= 0

Throws:

BadLocationException - some portion of the removal range was not a valid part of the document. The location in the exception is the first bad position encountered.

See Also:

DocumentEvent, DocumentListener, UndoableEditEvent, UndoableEditListener

insertString

void insertString(int offset,
                  String str,
                  AttributeSet a)
           throws BadLocationException

Parameters:

offset - the offset into the document to insert the content >= 0. All positions that track change at or after the given location will move.

str - the string to insert

a - the attributes to associate with the inserted content. This may be null if there are no attributes.

Throws:

BadLocationException - the given insert position is not a valid position within the document

See Also:

DocumentEvent, DocumentListener, UndoableEditEvent, UndoableEditListener

getText

String getText(int offset,
               int length)
        throws BadLocationException

Fetches the text contained within the given portion of the document.

Parameters:

offset - the offset into the document representing the desired start of the text >= 0

length - the length of the desired string >= 0

Returns:

the text, in a String of length >= 0

Throws:

BadLocationException - some portion of the given range was not a valid part of the document. The location in the exception is the first bad position encountered.

getText

void getText(int offset,
             int length,
             Segment txt)
      throws BadLocationException

  int nleft = doc.getDocumentLength();
   Segment text = new Segment();
   int offs = 0;
   text.setPartialReturn(true);
   while (nleft > 0) {
       doc.getText(offs, nleft, text);
       // do someting with text
       nleft -= text.count;
       offs += text.count;
   }

Parameters:

offset - the offset into the document representing the desired start of the text >= 0

length - the length of the desired string >= 0

txt - the Segment object to return the text in

Throws:

BadLocationException - Some portion of the given range was not a valid part of the document. The location in the exception is the first bad position encountered.

getStartPosition

Position getStartPosition()

Returns a position that represents the start of the document. The position returned can be counted on to track change and stay located at the beginning of the document.

Returns:

the position

getEndPosition

Position getEndPosition()

Returns a position that represents the end of the document. The position returned can be counted on to track change and stay located at the end of the document.

Returns:

the position

createPosition

Position createPosition(int offs)
                 throws BadLocationException

This method allows an application to mark a place in a sequence of character content. This mark can then be used to tracks change as insertions and removals are made in the content. The policy is that insertions always occur prior to the current position (the most common case) unless the insertion location is zero, in which case the insertion is forced to a position that follows the original position.

Parameters:

offs - the offset from the start of the document >= 0

Returns:

the position

Throws:

BadLocationException - if the given position does not represent a valid location in the associated document

getRootElements

Element[] getRootElements()

Returns:

the root element

getDefaultRootElement

Element getDefaultRootElement()

Returns the root element that views should be based upon, unless some other mechanism for assigning views to element structures is provided.

Returns:

the root element

render

void render(Runnable r)

Allows the model to be safely rendered in the presence of concurrency, if the model supports being updated asynchronously. The given runnable will be executed in a way that allows it to safely read the model with no changes while the runnable is being executed. The runnable itself may not make any mutations.

Parameters:

r - a Runnable used to render the model