paintComponent does not work if its called by the recursive function?

*SIMPLE EXPLANATION AS TO WHY YOU COULD ONLY SEE THE LAST UPDATE : *

A quote taken from Filthy Rich Clients by Chet Haase and Romain Guy

It is important to note that repaint requests get “coalesced,” or combined. 
So, for example, if you request a repaint and there is already one on the 
queue that has not yet been serviced, then the second request is ignored 
because your request for a repaint will already be fulfilled by the earlier 
request. This behavior is particularly helpful in situations where many
repaint requests are being generated, perhaps by very different situations 
and components, and Swing should avoid processing redundant requests and 
wasting effort.

Try your hands on this, and ask what is not clear to you :

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.*;

public class PointsExample
{   
    private CustomPanel contentPane;
    private Timer timer;
    private int x = 1;
    private int y = 1;
    private ActionListener timerAction = new ActionListener()
    {   
        public void actionPerformed(ActionEvent ae)
        {
            contentPane.set(x, y);
            x++;
            y++;
            if (x == 450)
                timer.stop();
        }
    };
    /*
     * This is just JFrame, that we be 
     * using as the Base for our Application.
     * Though here we are calling our
     * JPanel (CustomPanel), whose
     * paintComponent(...) method, we had
     * override.
     */
    private void createAndDisplayGUI()
    {
        JFrame frame = new JFrame("Locate Mouse Position");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        contentPane = new CustomPanel();
        frame.setContentPane(contentPane);  
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
        timer = new Timer(100, timerAction);
        timer.start();
    }

    public static void main(String\u005B\u005D args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new PointsExample().createAndDisplayGUI();
            }
        });
    }
}

class CustomPanel extends JComponent
{
    private int x;
    private int y;

    public void set(int a, int b)
    {
        x = a;
        y = b;
        repaint();
    }   

    @Override
    public Dimension getPreferredSize()
    {
        return (new Dimension(500, 500));
    }

    @Override
    public void paintComponent(Graphics g)
    { 
        g.clearRect(0, 0, getWidth(), getHeight());
        Graphics2D g2 =(Graphics2D) g;
        g2.fillOval(x, y, 4, 4);        
    }
}

Here is the code, that will allow you to have a look at your points while iterating inside a for loop, though this approach is highly discouraged, for many cons associated with it. Though try your hands on this instead of calling repaint() call paintImmediately(int …) or paintImmediately(Rectangle rect)

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import javax.swing.*;

public class PointsExample
{   
    private CustomPanel contentPane;
    private Timer timer;
    private int x = 1;
    private int y = 1;

    /*
     * This is just JFrame, that we be 
     * using as the Base for our Application.
     * Though here we are calling our
     * JPanel (CustomPanel), whose
     * paintComponent(...) method, we had
     * override.
     */
    private void createAndDisplayGUI()
    {
        JFrame frame = new JFrame("Locate Mouse Position");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        contentPane = new CustomPanel();
        frame.setContentPane(contentPane);  
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);

        for (int i = 0; i < 500; i++)
        {
            contentPane.set(x, y);
            x++;
            y++;
            if (x == 450)
                break;
        }
    }

    public static void main(String\u005B\u005D args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new PointsExample().createAndDisplayGUI();
            }
        });
    }
}

class CustomPanel extends JComponent
{
    private int x;
    private int y;

    public void set(int a, int b)
    {
        x = a;
        y = b;
        paintImmediately(0, 0, getWidth(), getHeight());

    }   

    @Override
    public Dimension getPreferredSize()
    {
        return (new Dimension(500, 500));
    }

    @Override
    public void paintComponent(Graphics g)
    { 
        super.paintComponent(g);
        g.fillOval(x, y, 4, 4);         
    }
}