在Application类中将SQLiteDatabase实例用作静态字段是一个好主意吗？

Question

I developing a dictionary android app. i am using a database in app to get word and it's meaning. is it a good way to use a static SQLiteDatabase in Application class and use it in some activities and classes?

public class App extends Application {
  public static SQLiteDatabase database;

  @Override
  public void onCreate() {
    super.onCreate();

    database = SQLiteDatabase.openOrCreateDatabase(
            Constants.MAIN_DB_PATH,
            null);
  }

and use it in this ways:

public class MainActivity extends AppCompatActivity {
    ...

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ...

        Cursor cursor = App.database.rawQuery(query, null);

        ...

    }
}

and:

public class MyClass{
    ...

    public MyClass() {
        ...

        Cursor cursor = App.database.rawQuery(query, null);

        ...
    }

}

Answer 1

Since you need only one instance of this object, this is a practicable approach. You can define the database:

public class Database{
    private static SQLiteDatabase localDatabase = null;
    private Database(){}

    public static SQLiteDatabase getLocalDatabase(){
        if (localDatabase == null){
            localDatabase = SQLiteDatabase.openOrCreateDatabase(...);
        }
        return localDatabase;
    }
}

In your activity code, you can use it like:

Database.getLocalDatabase().rawQuery(...); 

EDIT: To apply all rules of the Singleton-Pattern, also add a private & empty constructor, so you cannot instantiate the object accidentially.