How to get the EXACT middle of a screen, even when re-sized

Question

Ok, this sort of have 2 parts of the question.

1. When I make a JFrame, and draw something on it, even if I make the width 400, and make it so tha

Answer 1

This is what I use to centre a JFrame on screen, it simply retrieves the height and width of your monitor, then centres your frame

public static void moveToCenterScreen(JFrame frame) {
    Toolkit kit = frame.getToolkit();       
    GraphicsDevice[] gs = GraphicsEnvironment.getLocalGraphicsEnvironment().getScreenDevices();
    Insets in = kit.getScreenInsets(gs[0].getDefaultConfiguration());
    Dimension d = kit.getScreenSize();

    int max_width = (d.width - in.left - in.right);
    int max_height = (d.height - in.top - in.bottom);   

    frame.setLocation((int) (max_width - frame.getWidth()) / 2, (int) (max_height - frame.getHeight() ) / 2);
}