Saving Data on Android

separation of concerns
 to create a more structured application and improve its 
testability.
In Room, the DAOs are defined as 
interfaces
 or 
abstract classes
. The only difference 
between both implementations is that the abstract class can 
optionally
 accept a 
RoomDatabase
 instance, as a constructor parameter. They are also convenient for 
defining large database transactions, using the 
@Transaction
 annotation on a 
method, and calling multiple different methods within.
If you are wondering why DAOs are defined as abstract classes or interfaces, it is 
because Room takes care of creating each DAO implementation at compile time, by 
generating the business logic code for your definitions.
Note
: Remember that Room does not support database access on the main 
thread by default since performing long running operations such as database 
transactions might cause your app to freeze or crash. If you still want to take 
this risk, you will need to explicitly call 
allowMainThreadQueries()
 on your 
database builder.
But, alright, that's enough theory. Think about all the operations that you will need 
to perform on your database to make the DroidQuiz app work:
• You will need to