SharedPreferences pref = getSharedPreferences("a", Context.MODE_PRIVATE);
    if (pref.getBoolean("aa", false)) {
        Intent intent = new Intent(this, A2.class);
        startActivity(intent);
        finish();
    } else {


        SharedPreferences pref1 = getSharedPreferences("a", Context.MODE_PRIVATE);
        SharedPreferences.Editor edt = pref1.edit();
        edt.putBoolean("aa", true);
        edt.commit();

    }