SharedPreferences 클래스로 관리하기

 public class SharedUtil {
    public static void putString(Context context, String key, String value) {
        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);

        SharedPreferences.Editor editor = prefs.edit();

        editor.putString(key, value);
        editor.apply();
    }

    public static String getString(Context context, String key) {
        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
        return prefs.getString(key, null);
    }
}