Module java.desktop
Package javax.swing.text

Class AbstractDocument

java.lang.Object
javax.swing.text.AbstractDocument
All Implemented Interfaces:
Serializable, Document
Direct Known Subclasses:
DefaultStyledDocument, PlainDocument
public abstract class AbstractDocument extends Object implements Document, Serializable
An implementation of the document interface to serve as a basis for implementing various kinds of documents. At this level there is very little policy, so there is a corresponding increase in difficulty of use.

This class implements a locking mechanism for the document. It allows multiple readers or one writer, and writers must wait until all observers of the document have been notified of a previous change before beginning another mutation to the document. The read lock is acquired and released using the render method. A write lock is acquired by the methods that mutate the document, and are held for the duration of the method call. Notification is done on the thread that produced the mutation, and the thread has full read access to the document for the duration of the notification, but other readers are kept out until the notification has finished. The notification is a beans event notification which does not allow any further mutations until all listeners have been notified.

Any models subclassed from this class and used in conjunction with a text component that has a look and feel implementation that is derived from BasicTextUI may be safely updated asynchronously, because all access to the View hierarchy is serialized by BasicTextUI if the document is of type AbstractDocument. The locking assumes that an independent thread will access the View hierarchy only from the DocumentListener methods, and that there will be only one event thread active at a time.

If concurrency support is desired, there are the following additional implications. The code path for any DocumentListener implementation and any UndoListener implementation must be threadsafe, and not access the component lock if trying to be safe from deadlocks. The repaint and revalidate methods on JComponent are safe.

AbstractDocument models an implied break at the end of the document. Among other things this allows you to position the caret after the last character. As a result of this, getLength returns one less than the length of the Content. If you create your own Content, be sure and initialize it to have an additional character. Refer to StringContent and GapContent for examples of this. Another implication of this is that Elements that model the implied end character will have an endOffset == (getLength() + 1). For example, in DefaultStyledDocument getParagraphElement(getLength()).getEndOffset() == getLength() + 1 .

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 JavaBeans has been added to the java.beans package. Please see XMLEncoder.