Question

I use reading and writing to the database without any problems . But I can not find out the difference. I searched on Internet but it ‘s not quite clear. Can anyone tell me the difference? In which case should I use getWritableDatabase() or getReadableDatabase()?

Answer 1

Check the Reference

public synchronized SQLiteDatabase getReadableDatabase ()

Since: API Level 1

Create and/or open a database. This will be the same object returned
by getWritableDatabase() unless some problem, such as a full disk,
requires the database to be opened read-only. In that case, a
read-only database object will be returned. If the problem is fixed, a
future call to getWritableDatabase() may succeed, in which case the
read-only database object will be closed and the read/write object
will be returned in the future.

Like getWritableDatabase(), this method may take a long time to return, so you should not call it from the application main thread, including from ContentProvider.onCreate().
Returns

a database object valid until getWritableDatabase() or close() is called. 

Throws
SQLiteException if the database cannot be opened

public synchronized SQLiteDatabase getWritableDatabase ()

Since: API Level 1

Create and/or open a database that will be used for reading and
writing. The first time this is called, the database will be opened
and onCreate(SQLiteDatabase), onUpgrade(SQLiteDatabase, int, int)
and/or onOpen(SQLiteDatabase) will be called.

Once opened successfully, the database is cached, so you can call this
method every time you need to write to the database. (Make sure to
call close() when you no longer need the database.) Errors such as bad
permissions or a full disk may cause this method to fail, but future
attempts may succeed if the problem is fixed.

Database upgrade may take a long time, you should not call this method from the application main thread, including from ContentProvider.onCreate().
Returns

a read/write database object valid until close() is called 

Throws
SQLiteException if the database cannot be opened for writing