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, 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, String, 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(Object)
• putProperty(Object, Object)

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