Solution to one Design Puzzle in Head First Design Pattern

I am reading Head First Design Pattern. It is a great book.

Generally, I don't like exercises in a book which don't have answers provided. I have run into the design puzzle on page 468. At first sight, I knew that I should use state pattern. I have never applied state pattern in real software work before. So I took this exercise as an opportunity to practice state pattern. Here is my solution.

State.java

package headfirst.proxy.virtualproxy;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public interface State {
 public int getIconWidth();
 public int getIconHeight();
 public void paintIcon( Component c, Graphics g, int x, int y );
}

NullState.java

package headfirst.proxy.virtualproxy;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class NullState implements State {

    private ImageProxy proxy;
    private Thread retrievalThread;
    private URL imageURL;
 boolean retrieving = false;

    public NullState( ImageProxy p, URL url) {
        proxy = p;
        imageURL = url;
    }

    public int getIconWidth() {
        return 800;
    }

    public int getIconHeight() {
        return 600;
    }

    public void paintIcon( final Component c, Graphics g, int x, int y ) {
        g.drawString("Loading CD cover, please wait...", x+300, y+190);
        if (!retrieving) {
            retrieving = true;
            retrievalThread = new Thread(new Runnable() {
                public void run() {
                    try {
                        ImageIcon imageIcon = new ImageIcon(imageURL, "CD Cover");
                        proxy.setState( new ImageState( imageIcon )  );
                        c.repaint();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });
            retrievalThread.start();
        }
    }
}

ImageState.java

package headfirst.proxy.virtualproxy;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ImageState implements State {
    
    private ImageIcon imageIcon;
    
    public ImageState( ImageIcon i ) {
        imageIcon = i;
    }

    public int getIconWidth() {
        return imageIcon.getIconWidth();
    }

    public int getIconHeight() {
        return imageIcon.getIconHeight();
    }

    public void paintIcon( final Component c, Graphics g, int x, int y ) {
        imageIcon.paintIcon(c, g, x, y);
    }
}

ImageProxy.java

package headfirst.proxy.virtualproxy;

import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ImageProxy implements Icon {

    private NullState ns;
    private State state;
     
 public ImageProxy(URL url) {
        ns = new NullState( this, url );
        state = ns;
    }
     
 public int getIconWidth() {
        return state.getIconWidth();
 }
 
 public int getIconHeight() {
        return state.getIconWidth();
 }
     
 public void paintIcon(final Component c, Graphics  g, int x,  int y) {
        state.paintIcon( c, g, x, y);
 }

    public void setState( State s ) 
    {
        state = s;
    }
}