super.addNotify()

[icedust]

I'm reading Killer Game Programming in Java, however I'm confused about something, and that is how addNotify works exactly.

In an effort to understand, I did this:

public class GamePanel extends JPanel implements Runnable
{

	// some variables .......
	public GamePanel()
	{
		System.out.println("Constructor started");
		setBackground(Color.white);
		setPreferredSize(new Dimension(PWIDTH, PHEIGHT));

		// create game components
		// ..
		System.out.println("Constructor ended");
	} // END OF GAMEPANEL

	@Override
	public void addNotify()
	{
		System.out.println("addNotify started");
		super.addNotify();
		startGame();
		System.out.println("addNotify ended");
	}
// some more stuff, not relevant
}

The JFrame:

public class Main extends JFrame
{
	
	public Main()
	{
		System.out.println("Constructor main started");
		setTitle("game");
		setSize(500, 400);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		add(new GamePanel());
		try
		{
			Thread.sleep(3000);
			System.out.println("setVisible getting called");
		} catch (InterruptedException e)
		{
			e.printStackTrace();
		}
		setVisible(true);
		try
		{
			System.out.println("setVisible ended");
			Thread.sleep(3000);
		} catch (InterruptedException e)
		{
			e.printStackTrace();
		}
		System.out.println("Constructor main ended");	
	}
	
	public static void main(String[] args) {
		new Main();
	}

}

The result was this:

Constructor main started
Constructor started
Constructor ended
(*Imagine a 3 second delay here*)
setVisible getting called
addNotify started
addNotify ended
setVisible ended
(*Imagine another 3 second delay*)
Constructor main ended


So it is clear addNotify gets called only when setVisible() of the JFrame is called, and that is desired I suppose. But why? GamePanel isn't an subclass of Main, is it? Maybe I'm just tired, but I dont get how this works exactly

[KevinWorkman]

GamePanel is a subclass of JPanel. The JPanel is added to the JFrame, so the JPanel becomes visible when the JFrame becomes visible.