Simple exercise on Room Database
How to design and construct an app using some of the Android Architecture Components. You'll use Room, ViewModel, and LiveData.
1-Create an app with an Activity that displays words in a RecyclerView.
2-Create an Entity that represents word objects.
3-Define the mapping of SQL queries to Java methods in a DAO (data access object).
4-Use LiveData to make changes to the data visible to the UI, by way of observers.
5-Add a Room database to the app for persisting data locally, and initialize the database. 6-Abstract the data backend as a Repository class with an API that is agnostic to how the data is stored or acquired.
7-Use a ViewModel to separate all data operations from the UI. 8-Add a second Activity that allows the user to add new words.