We have talked a bit about the structure of our code; that we write classes, and within those classes we have methods that contain our code. We also know that when we want the code within a method to run (be executed), we call that method by using its name.
Also, in Chapter 2, Java - First Contact, we learned that Android itself calls the onCreate method just before the app is ready to start. We saw this when we outputted to the logcat and used the Toast class to send a pop-up message to the user.
What we will look at now is what happens throughout the lifecycle of every app we write: when it starts and ends, as well as a few stages in between. And what we will see is that Android actually interacts with our app on numerous occasions, each and every time it is run.
It does so by calling methods that are contained within the Activity class. Even if the method is not visible within our Java code, it is still being called by Android at the appropriate time...