DrJava offers the ability to generate JavaDoc documentation for the user's java files. For information about what JavaDoc is and how to format your comments to take advantage of it, see http://www.oracle.com/technetwork/java/javase/documentation/index-137868.html.
To generate JavaDoc for all files in the same directories as your open files, click the "JavaDoc" button on the toolbar. You will then be asked where you want to save the javadoc files. Select a location and click OK. Your JavaDoc will be generated for you.
To generate JavaDoc for one specific file, select it from the open list of files and right click and select "Preview JavaDoc" for current Document. You will be able to view the JavaDoc for that file in the JavaDoc viewer.