HabitRoomDatabase.kt

@Database(entities = {Habit.class}, version = 1)
public abstract class HabitRoomDatabase extends RoomDatabase{

  public abstract HabitDao wordDao();

  //SINGLETON
  private static HabitRoomDatabase INSTANCE;

  static HabitRoomDatabase getDatabase(final Context context) {
    if (INSTANCE == null) {
      synchronized (HabitRoomDatabase.class) {
        if (INSTANCE == null) {
          INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
              HabitRoomDatabase.class, "habit_database")
              .build();
        }
      }
    }
    return INSTANCE;
  }