How can I program a rotating circular animation such as this one (picture attached)? Android

I am developing an app & just built its logical part. Now I want to design this app like in famous timer apps.for examples:

The thing I want is the outer Circle that fills with every trigger of some event or with increment of number. I actually don't know that is it animation part (like to be built in flash or what) or just possible by coding in android itself using its inbuilt properties and features. So anybody if tell explain me what tools are used or any reference tutorial that can explain things from bottom. I really don't know any thing of designing . Any code for this??