Data Storage: SQLite and Preferences

Storage Options

• SharedPreferences - small key-value settings.
• Internal storage - private files inside the app sandbox.
• SQLite database - structured relational data.
• External storage - shared public files on the SD card.

SharedPreferences

Save and read simple settings with one instance:

SharedPreferences prefs = getSharedPreferences("app_settings", MODE_PRIVATE);
prefs.edit().putString("user", "nisha").apply();
String user = prefs.getString("user", "");

Internal Storage

Read and write private files:

FileOutputStream fos = openFileOutput("notes.txt", MODE_PRIVATE);
fos.write(text.getBytes());
fos.close();

External Storage

Files visible to other apps (needs WRITE_EXTERNAL_STORAGE permission):

File dir = Environment.getExternalStorageDirectory();

SQLite Database

Create tables with SQLiteOpenHelper and run CRUD through a database object:

db.execSQL("CREATE TABLE IF NOT EXISTS students (id INTEGER PRIMARY KEY, name TEXT, grade INTEGER)");
ContentValues v = new ContentValues();
v.put("name", "Nisha"); v.put("grade", 10);
db.insert("students", null, v);

Key Points

• Use SharedPreferences for settings, SQLite for structured data.
• Internal storage is private; external storage is world-readable.
• CursorAdapter links SQLite queries to ListViews.