public class share {
    public static void saveInfo(Context context,String username,String password)
    {
        SharedPreferences sp = context.getSharedPreferences("config", context.MODE_PRIVATE);
        Editor editor = sp.edit();
        editor.putString("username", username);
        editor.putString("password", password);
        editor.commit();
    }
}

SharedPreferences sp = getSharedPreferences("config", MODE_PRIVATE);
        String username = sp.getString("username", "");
        String password = sp.getString("password", "");
        usernameText.setText(username);
        passwordText.setText(password);