How can I use SharedPreferences on Android Studio to save some data like the value of a boolean?

```
SharedPreferences.Editor editor = getSharedPreferences(MY_PREFS_NAME,MODE_PRIVATE).edit();
    editor.putBoolean("firststart",false);
    editor.apply();
    SharedPreferences prefs = getSharedPreferences(MY_PREFS_NAME,MODE_PRIVATE);
    boolean firstStart= prefs.getBoolean("firststart",false);
    if (!firstStart) {
        Intent intent12 = new Intent(getApplicationContext(),FirstStart.class);
        startActivity(intent12);
        prefs.getBoolean("firststart",true);
    }
    else if (firstStart) {

    }

```

If I use this code everytime I create the activity the value of the boolean return false and then true.
How can I resolve this problem and don't lose the data?