[디자인패턴] 프록시 패턴, proxy pattern

http://en.wikipedia.org/wiki/Proxy_pattern

프록시 패턴은 어떤 객체에 대한 접근을 제어하기 위한 용도로 대리인이나 대변인에 해당하는 객체를 제공하는 패턱

import java.util.*;
 
interface Image {
    public void displayImage();
}
 
//on System A 
class RealImage implements Image {
    private String filename;
    public RealImage(String filename) { 
        this.filename = filename;
        loadImageFromDisk();
    }
 
    private void loadImageFromDisk() {
        System.out.println("Loading   " + filename);
    }
 
    public void displayImage() { 
        System.out.println("Displaying " + filename); 
    }
}
 
//on System B 
class ProxyImage implements Image {
    private String filename;
    private Image image;
 
    public ProxyImage(String filename) { 
        this.filename = filename; 
    }
    public void displayImage() {
        if (image == null)
        {
           image = new RealImage(filename);
        } 
        image.displayImage();
    }
}
 
class ProxyExample {
    public static void main(String[] args) {
        Image image1 = new ProxyImage("HiRes_10MB_Photo1");
        Image image2 = new ProxyImage("HiRes_10MB_Photo2");     
 
        image1.displayImage(); // loading necessary
        image2.displayImage(); // loading necessary
    }
}