Activity Lifecycle Methods onCreate() Called when activity first created onRestart() Called after activity stopped, prior to restarting onStart() Called when activity is becoming visible to user onResume() Called when activity starts interacting with user onPause() Called when a previous activity is about to resume onStop() Called when activity no longer visible to user onDestroy() Final call received before activity is destroyed ----------------- Creational patterns: Builder (e.g. AlertDialog.Builder) Dependency Injection (e.g. Dagger 2) Singleton Structural patterns: Adapter (e.g. RecyclerView.Adapter) Facade (e.g. Retrofit) Behavioral patterns: Command (e.g. EventBus) Observer (e.g. RxAndroid) Model View Controller Model View ViewModel (similar to the MVC pattern above)