Android places very strict limits on the use of threads in applications: every application has a main thread, where all user-interface related code must run, but any long-running code will cause an error. Any attempt at networking on the main thread will result in a NetworkOnMainThreadException immediately, as networking by its very nature will block the main thread for too long, making the application unresponsive.
This means most tasks that you will want to perform should take place on a background worker thread. This will also provide you with a form of isolation from the user interface, as typically you will capture the user interface state on the main thread, pass the state to the background thread, process the event and then, send the result back to the main thread where you will update the user interface. How do we know that the state we capture will be consistent? The answer is that because user interface code can only run on the main thread, while you read the...