Data is not being written in Firebase Realtime Database from Android App

I want to write data in Firebase Realtime Database from Android.I did the following things.

1. Created Project in firebase

2. Configured and downloaded the json file and pasted in the app directory

3. Did all others stuffs.

4. EDITED THE RULES CORRECTLY

Then I am trying to run the most simplest code provided in the docs

FirebaseDatabase database = FirebaseDatabase.getInstance();
    DatabaseReference myRef = database.getReference("message");

    myRef.setValue("Hello, World!");

Still not working. The database is still showing empty. Somebody please help. Thank you