SingletonApp

Maybe below contain a lot of obvious questions... I went through a lot of reading but I could not yet answer.

I am trying to create an application that consists of a basic service and a user interface. The background service would be starts automatically when you start. So I used Singleton to develop the application.

Code is attached and it is very simple. There is no cleanup action in the example below.

The SingletonAppcontains a static variable that is the SingletonApp itself, and a method "createInstance".

When the entry point is called, it calls createInstance. If the _instance is null, create a new instance of SingletonApp, otherwise the existing one is reused.

Issues related to the:

1: whenever I click the icon, a new instance is always created and a new thread is started. Why the _instance is always null, even if it's a static variable?

2: I read some examples on the use of RuntimeStore, but it seems that my application does not need to store the application to the RuntimeStore. Below is written without using RuntimeStore intentionally. If I use RuntimeStore, my problem is simply not able to bring the screen interface by calling requestForeground(), I guess I missed something.

3: there are a few examples that check the args (autostartup, gui) to hand. Where are these passing arguments? Is the device / Simulator would be automatic passes these arguments according to different scenarios?

public class SingletonApp extends UiApplication {

    private static SingletonApp _instance = null;

    private SingletonApp() {
        pushScreen(new SingletonScreen());
    }

    public static synchronized SingletonApp createInstance() {

        if (_instance == null) {
            System.out.println("===== SingletonApp Creating Instance");
            _instance = new SingletonApp();
            _instance.enterEventDispatcher();
        } else {
            _instance.pushScreen(new SingletonScreen());
        }

        return _instance;

    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        SingletonApp app = createInstance();

    }

}

public class SingletonScreen extends MainScreen implements Runnable {

    public SingletonScreen() {
        setTitle("Hello World!");
        Thread t = new Thread(this);
        t.start();
    }

    public void run() {
        while (true) {
            int nCount = 0;
            try {
                System.out.println("===== Thread is running: " + ++nCount);
                Thread.sleep(5000);

            } catch (Exception e) {
                System.out.println("===== Exception@Run: " + e.getMessage());
            }
        }
    }
}