if you’re using java to code then you must also create UML diagram. to do this you can download a plugin for eclipse here and after that put the plugin in eclipse’ plugin directory. after that run eclipse
To create a new, empty UMLet diagram in Eclipse,
1. select a directory in the Eclipse resource navigator;
2. select “File/New/Other..” from the menu or the context menu; in the subsequent wizard,
3. select “UMLet/Diagram”.
this is the screenshot of what you will see in your eclipse IDE
there are many tools available to do UML though, you can find another one here
and there you goes. it will install a UML including all the use case, class diagram and also sequence diagram. all you need to complete your object oriented task.