Can you explain the concept of the proxy pattern and its purpose in programming?

The "Proxy" pattern is a structural design pattern that provides a surrogate object for another object. The proxy controls access to the real object, allowing additional actions to be performed when methods are called.

Purpose of the proxy:

• Lazy initialization (lazy loading).
• Access control (e.g., permission checks).
• Logging calls.
• Caching results.
• Remote access (e.g., in RMI).

Example in Java:

interface Image {
    void display();
}

class RealImage implements Image {
    private String filename;

    public RealImage(String filename) {
        this.filename = filename;
        loadFromDisk();
    }

    private void loadFromDisk() {
        System.out.println("Loading " + filename);
    }

    public void display() {
        System.out.println("Displaying " + filename);
    }
}

class ProxyImage implements Image {
    private RealImage realImage;
    private String filename;

    public ProxyImage(String filename) {
        this.filename = filename;
    }

    public void display() {
        if (realImage == null) {
            realImage = new RealImage(filename); // load on first call
        }
        realImage.display();
    }
}

// Usage:
Image image = new ProxyImage("photo.jpg");
image.display(); // loads and displays
image.display(); // just displays

Here, ProxyImage delays loading the actual image until the first call to display().