We have talked a bit about the structure of our code: we know that we can write classes, and within those classes we have methods, and these methods contain our code that gets things done. 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, First Contact: Java, XML and the UI Designer, we learned that Android itself calls the onCreate method just before the app is ready to start. We saw this when we output to the logcat and used the Toast class to send a pop up message to the user.
What we will look at in this chapter is what happens throughout the lifecycle of every app we write; when it starts and ends, as well as a few stages in-between as well. And what we will see is that Android interacts with our app on numerous occasions each time it is run.