Tool to generate class diagrams.

Hello,

While writing design document(tech specification doc) ,I need to create class diagrams for few classes which already exist and need some modifications.
Is there any tool/software available to generate class diagrams using existing classes??
Please suggest.

Thanks

There are a number of tools, some of them stand alone, some plug into your development environment.

You need first to reverse the java code then to display it into a class diagram.
Finally changing the diagram will also change the code using live code a model synchronization.

The only tool which is capable of doing it is EclipseUML Omondo because this tool is focused on Java and live code and model synchronization while other tools are more MDD oriented. I mean that you model then generate code but you don't upload java code into model and merge it with the diagram change.
A good example to read is: http://www.forum-omondo.com/documentation_eclipseuml_2008/reverse/reverse/reverse_engineering_example.html

Rational Applicatio Developer / Rational Rose have similar capabilities.

No, it doesn't because in the RSA Java version you are live synchronized permanently and model is included as tag in your code !!
A good study has been published at : http://www.tutorial-omondo.com/RSA7_versus_EclipseUML/RSA_EclipseUML_features_chart.html
Have a look then I am sure you will understand why EclipseUML is better