Why Graphics objects don't overlap.

Code java:

---

	class FirstDrawPanel extends JPanel
	{	
		public void paintComponent(Graphics g)
		{
			g.setColor(Color.WHITE); 
			g.fillRect(0, 0, this.getWidth(), this.getHeight());
			g.setColor(Color.BLUE);
			g.fillOval(xCoord, yCoord, 50, 50);
		}
	} 
	class SecondDrawPanel extends JPanel
	{
		public void paintComponent(Graphics g)
		{
			g.setColor(Color.WHITE); 
			g.fillRect(0, 0, this.getWidth(), this.getHeight());
			g.setColor(Color.ORANGE);
			g.fillRect(xCoord, 0, 50, 50);
		}
	}

---

I want to know why the two Graphics objects don't overlap each other.

Can anyone help?