How to generate UML diagrams (especially sequence diagrams) from Java code?

Question

How can I generate UML diagrams (especially sequence diagrams) from existing Java code?

Answer 1

ObjectAid UML Explorer

Is what I used. It is easily installed from the repository:

Name:     ObjectAid UML Explorer Location: http://www.objectaid.com/update/current 

And produces quite nice UML diagrams:

Description from the website:

The ObjectAid UML Explorer is different from other UML tools. It uses the UML notation to show a graphical representation of existing code that is as accurate and up-to-date as your text editor, while being very easy to use. Several unique features make this possible:

• Your source code and libraries are the model that is displayed, they are not reverse engineered into a different format.
• If you update your code in Eclipse, your diagram is updated as well; there is no need to reverse engineer source code.
• Refactoring updates your diagram as well as your source code. When you rename a field or move a class, your diagram simply reflects the changes without going out of sync.
• All diagrams in your Eclipse workspace are updated with refactoring changes as appropriate. If necessary, they are checked out of your version control system.
• Diagrams are fully integrated into the Eclipse IDE. You can drag Java classes from any other view onto the diagram, and diagram-related information is shown in other views wherever applicable.