Why is getWritableDatabase() necessary to create a SQLite database?

Question

I want to create a SQLite database.
So I followed a tutorial and I have these two lines in my MainActivity that create the database.

LugaresDB lugaresDB = new LugaresDB(getApplicationContext());
SQLiteDatabase db = lugaresDB.getWritableDatabase();

My question: I expected just the first line to create the database, but it doesn't create it.
I have to add the second line. Why?

The first line creates an object, not a file. Similarly, `new File(...)` creates an object, not a file. — CommonsWare, Dec 20 '17 at 14:52

score 4 · Accepted Answer · answered Dec 20 '17 at 14:51

Because that's how the framework is implemented.

It's not possible to say exactly why it is implemented as such, but generally it is a good design idea to follow principles of single responsibility and least astonishment: a constructor is only responsible for object instance initialization. Any other actions such as actually opening the database with file I/O are undesirable side effects. These other actions are better modelled as methods with verb in their name.

score 0 · Answer 2 · answered Dec 20 '17 at 14:52

Because that is the way the class is implemented. Your LugaresDB seems to be a subclass of SQLiteOpenHelper. The first line creates a helper object of class SQLiteOpenHelper which can be used to create either a read-only or writable instance of SQLiteDatabase, which is what the second line does.

Why is getWritableDatabase() necessary to create a SQLite database?

2 Answers2

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