Im currently trying to teach myself a bit of Java and was looking at a tutorial with the following code:

package painting;

import javax.swing.SwingUtilities;

import javax.swing.JFrame;

import javax.swing.JPanel;
import javax.swing.BorderFactory;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;

public class SwingPaintDemo2 {

  public static void main(String[] args) {

  SwingUtilities.invokeLater(new Runnable() {

  public void run() {

  createAndShowGUI();

  }

  });

  }

  private static void createAndShowGUI() {

  System.out.println("Created GUI on EDT? "+

  SwingUtilities.isEventDispatchThread());

  JFrame f = new JFrame("Swing Paint Demo");

  f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

   f.add(new MyPanel());
  f.pack();

  f.setVisible(true);

  }

}

class MyPanel extends JPanel {

  public MyPanel() {
  setBorder(BorderFactory.createLineBorder(Color.black));
  }

  public Dimension getPreferredSize() {
  return new Dimension(250,200);
  }

  public void paintComponent(Graphics g) {
  super.paintComponent(g);

  // Draw Text
  g.drawString("This is my custom Panel!",10,20);
  } 
}

What this does is creates a frame and displays the text "this is my custom panel" but what I dont get is how is the text displayed.  I know I create the panel MyPanel with one constructor and two methods, getPreferredSize() and paintComponent().  I understand paintComponent is responsible for printing the text "this is my custom Panel" on to the panel but when I am adding the panel the code simply calls the constructor f.add(new MyPanel());.  This constructor only creates the border.  Nowhere in the code am I calling the paintComponent method so how is the code here getting executed?

Sorry if this is a silly question but I just dont seem to get it.

Thanks for any help I may get.