Rectangle getting drawn in the wrong spot

I am creating a game inside a JFrame (854 x 480). I am trying to draw a Rectangle in the upper right hand corner of the screen. like so:

int x, y;
Rectangle rect;

public Foo() {
    x = 0;
    y = 0;
    
    rect = new Rectangle(x, y, 63, 27);
}

....

public void draw(Graphics g) {
    g.drawRect(rect.x, rect.y, rect.width, rect.height);
}

But when I do this, the box gets drawn off the screen (x co-ords are right, but y co-ords too high :

When I change the y co-ords to 27 (the height of the rectangle), it moves down to where I want it to go:

Any idea why this is happening? Or how to fix it?

Do you override the paint(..) method of your JFrame? The coordinates seem to be in the coordinate space of the window/JFrame, where 0/0 includes the non-client area (the close box, title bar and so on).

You should create a separate component and add this to the content pane of your main frame - just a very tiny example - note that I am using paintComponent(..):

public static class MyPanel extends JPanel {
    @Override
    protected void paintComponent(final Graphics g) {
        super.paintComponent(g);
        final Graphics2D g2 = (Graphics2D) g;
        g2.setColor(Color.BLUE);
        g2.draw(new Rectangle2D.Float(8,8, 128, 64));
    }

}

Add to JFrame content pane (use default or custom LayoutManager):

public class MyFrame extends JFrame {
    public MyFrame() {
       ...
       // since JDK 1.4 you do not need to use JFrame.getContentPane().add(..)
       this.add(new MyPanel());
    }
}

This should do the trick. Here's the corresponding section of the Java SE tutorial.