Proxy - Design Patterns Java - page 97

public ImageIconProxy(String filename)
{
super(ABSENT.getImage());
this.filename = filename;
}
public void load(JFrame callbackFrame)
{
this.callbackFrame = callbackFrame;
current = LOADING;
callbackFrame.repaint();
new Thread(this).start();
}
public void run()
{
current = new ImageIcon(filename);
callbackFrame.pack();
}
public int getIconHeight()
{
// challenge!
}
public int getIconWidth()
{
// challenge!
}
public synchronized void paintIcon(
Component c, Graphics g, int x, int y)
{
// challenge!
}
}
CHALLENGE 11.1
An ImageIconProxy object accepts three image display calls that it must pass on
to the current image. Write the code for getIconHeight() , getIconWidth() ,
and paintIcon() for the ImageIconProxy class.
Suppose that you get the code working for this small demonstration application. Before you
build the real application, which has more than just a Load button, you hold a design review,
and the fragility of your design comes to light.
As with many proxies, there is a dangerous dependency between ImageIcon and
ImageIconProxy . The current design assumes that you have correctly ascertained, or
guessed, the right methods to override. Even if you have, the ImageIcon class can change in
a future release and break your code. You and the design review team decide to rework your
approach.