Help required on writing a new Check

Hi Friends,

I am a new user of Checkstyle. I am using Checkstyle 4.4 on Windows XP with
JDK1.6 and Ant 1.7
I've to write a check which can identify the java classes which implements
java.io.Serializable and further I've to check that whether they have
defined a serialVersionUID field or not.
My approach is to write a new check class which extends
com.puppycrawl.tools.checkstyle.api.AbstractFileSetCheck.
Right now I just know a little bit about how to traverse and check for
conditions inside a specific Java file using public void
visitToken(DetailAST aAST)  method.
However, I don't know about the following scenario:
(i) How to traverse through a set of files?
(ii) How to check these files for a particular condition (like a class which
implements a particular interface etc.) and select files on the basis of
this condition.?
(iii) How to get a DetailAST for a file selected in (ii) step?

I'll really like to learn about the basic concepts of writing new checks.
Any help, probably in the form of some other similar type of check's code /
documentation / or concept, is greatly appreciated.

Best Regards,
Nitin Bhardwaj

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