pattern and design - proxy patter the basic

In this post, we are going to review the most commonly used patter, which is called the proxy patter, which is widely used . THe official definition you can find from the wikipedia, here is the link

Proxy Pattern

you can find the definition and some of the high level architecture of it from the official twiki page.

here is the code.

interface Image {
    public void displayImage();
}

//on System A 
class RealImage implements Image {

    private String filename = null;
    /**
     * Constructor
     * @param FILENAME
     */
    public RealImage(final String FILENAME) { 
        filename = FILENAME;
        loadImageFromDisk();
    }

    /**
     * Loads the image from the disk
     */
    private void loadImageFromDisk() {
        System.out.println("Loading   " + filename);
    }

    /**
     * Displays the image
     */
    public void displayImage() { 
        System.out.println("Displaying " + filename); 
    }

}

//on System B 
class ProxyImage implements Image {

    private RealImage image = null;
    private String filename = null;
    /**
     * Constructor
     * @param FILENAME
     */
    public ProxyImage(final String FILENAME) { 
        filename = FILENAME; 
    }

    /**
     * Displays the image
     */
    public void displayImage() {
        if (image == null) {
           image = new RealImage(filename);
        } 
        image.displayImage();
    }

}

class ProxyExample {

   /**
    * Test method
    */
   public static void main(String[] args) {
        final Image IMAGE1 = new ProxyImage("HiRes_10MB_Photo1");
        final Image IMAGE2 = new ProxyImage("HiRes_10MB_Photo2");     

        IMAGE1.displayImage(); // loading necessary
        IMAGE1.displayImage(); // loading unnecessary
        IMAGE2.displayImage(); // loading necessary
        IMAGE2.displayImage(); // loading unnecessary
        IMAGE1.displayImage(); // loading unnecessary
    }

}