Saving Data on Android

data 
synchronization
 and 
subcriber mechanisms
 instead of typical HTTP requests, 
which allows you to build more flexible real-time apps, easily, with less effort and 
without the need to worry about networking code.
Many apps become unresponsive when you lose the network connection. Realtime 
Database provides great 
offline
 support because it keeps an internal cache of all the 
data you've queried. When there's no Internet connection, the app uses the data from 
the cache, allowing apps to remain responsive. When the device connects to the 
Internet, the Realtime Database synchronizes the local data changes with the remote 
updates that occurred while the client was offline, resolving any conflicts 
automatically.
Client devices access the Realtime Database