Data Persistence

File I/O
Shared Preferences
SQLite Database
Content Providers

File I/O

Write to a file:

FileOutputStream fos = null;

fos = openFileOutput(FILE_NAME, MODE_PRIVATE);

fos.write(text.getBytes());

Toast.makeText(this, 
    "Saved to " + getFilesDir() + "/" + FILE_NAME , Toast.LENGTH_SHORT)
    .show();

if(fos != null) {
        fos.close();
}

Read from a file:

FileInputStream fin = null;

fin = openFileInput(FILE_NAME);

InputStreamReader inputStreamReader = new InputStreamReader(fin);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
StringBuilder sb = new StringBuilder();

while((String text = bufferedReader.readLine()) != null) {
    sb.append(text).append("\n");
}

if(fin != null) {
    fin.close();
}

Shared Preference

It is simple key-value storage system that allows you to store and retrieve primitive data types (such as boolean, float, int, long, String) in a persistent way.

SharedPreferences are commonly used for saving application settings, user preferences, and other small pieces of data that need to be persisted between app sessions.

Writing to Shared Preference

SharedPreferences prefs = getSharedPreferences("login", MODE_PRIVATE);
SharedPreferences.Editor editor = prefs.edit();
editor.putBoolean("flag", true);
editor.apply();

Reading from Shared Preference

SharedPreferences prefs = getSharedPreferences("login", MODE_PRIVATE);
boolean check = sharedPreferences.getBoolean("flag", false);    
                                // getBoolean(key, defaultValue)

Last modified: 05 February 2026