Develope a java activity and xml page for an android app

I am developing an Android app and would like a timer that counts down in Hours, Minutes and Seconds. The timer would be set in 00:00:00 form by the user. When the timer is finished, there will be a message displayed or a sound played.

I would like the java and xml file so that I can add it to my current Eclipse project and simply set up a button to start the timer activity. This should be an easy task for those of you who are skilled.

Thank you