room_init.java

@Database(entities = {SomeEntity.class}, version = 1)
public abstract class Database extends RoomDatabase {
    private static Database instance;

    public abstract SomeDao dao();

    public static synchronized NoteDatabase getInstance(Context context) {
        if (instance == null) {
            instance = Room.databaseBuilder(context.getApplicationContext(), Database.class, "database").
                    fallbackToDestructiveMigration().
                    .build();
        }
        return instance;
    }
}