Best procedure to implement observer design pattern in Android -

This may be a stupid question, but knowing best practices and APIs for implementing supervisor design patterns in Android Wants
In my application, say that I have classes which implement BLL, model, UI and web service handling. Now a screen application hits the web service and receives value that will update the model class values. If Blal classes want an update value instead of checking each value, bll would like to receive notifications for all updates
Different modules should be able to register and be notified for these types of event updates.
What is the best solution to get the same?

If you want to get notifications for specific Use the event, the observer interface in Android, see it in