Java Singleton

NotificationUtility.java

	
public NotificationUtility {
  private static NotificationUtility instance;
  
  // singleton GSON object, to be used by any other class (dirty)
  public Gson gson = new Gson();
  // private singleton list of notifications, to be accessed from BackgroundService
  private static List<Notification> notifications;
  
  public static NotificationUtility getInstance() {
    return (instance == null) ? new NotificationUtility() : instance;
  }
 
  public List<Notification> getList() {
    // Ensure read only occured if no existing list exists
    if (notifications == null) {
      String storedNotifs = readFromStorage(location);
      notifications = gson.fromJson(storedNotifs, new TypeToken<List<Notification>>(){}.getType());
    }
    return notifications
  }
 
  public void store(String apiResponse) {
    NotificationUtility.notifications = gson.fromJson(apiResponse, new TypeToken<List<Notification>>(){}.getType());
    writeToStorage(apiResponse);
  }
 
  public void append(String socketResponse) {
    Notification incoming = gson.fromJSON(socketResponse, Notification.class);
    List<Notification> tempList = getList();
    if (tempList.contains(incoming) {
      update(tempList);
    } else {
      // insert new notif to first position
      tempList.add(0, incoming);
    }
    String updatedNotifs = gson.toJSON(tempList);
    writeToStorage(updatedNotifs);
    // Override existing global list of notifications
    notifications = tempList;
  }
}