Java Swing, 2nd Edition

The Document Model

The Document is the M part of the MVC (Model-View-Controller) architecture for all of Swing’s text components. It is responsible for the text content of the component as well as relevant style information for text components that support styled text. The Document model must be simple enough to be used by JTextField, but powerful and flexible enough to be used by JTextPane and JEditorPane. Swing accomplishes this by providing the classes and interfaces shown in Figure 22-7.

Figure 22-7. High-level Document class diagram

Basically, a Document partitions its content into small pieces called Elements. Each Element is small enough that its style information can be represented by a single AttributeSet. The Elements are organized into a tree structure^[22] with a single root.

Swing provides the Document interface, which doesn’t support styled text, and the StyledDocument interface, which does. But note that there is no StyledElement interface. Swing provides a single Element interface that does support style. The simpler document types (such as PlainDocument, which JTextField and JTextArea use by default) use Elements but don’t assign any style information to them.

The Element Interface

The Element interface is used to describe a portion of a document. But note that an Element does not actually contain a portion of the document; it just defines a way of structuring a portion. ...