Facade Pattern | Structural Patterns

1. Introduction

The Facade Pattern is a structural design pattern that provides a simplified interface to a complex system of classes, libraries, or frameworks. It acts as a front-facing interface masking more complex underlying or structural code.

This pattern is particularly useful in managing and simplifying interactions with complex subsystems.

2. Key Concepts

Provides a unified interface to a set of interfaces in a subsystem.
Decouples a client from the complex subsystem.
Simplifies usage of complex systems, promoting easier integration.

Note: The Facade Pattern does not prevent the client from using the subsystem classes directly. It simply provides a simpler way to interact with them.

3. Implementation

Below is a simple implementation of the Facade Pattern in a home theater system:


class Amplifier {
    public void on() { System.out.println("Amplifier is on"); }
    public void off() { System.out.println("Amplifier is off"); }
}

class DVDPlayer {
    public void on() { System.out.println("DVD Player is on"); }
    public void play(String movie) { System.out.println("Playing " + movie); }
}

class Projector {
    public void on() { System.out.println("Projector is on"); }
    public void off() { System.out.println("Projector is off"); }
}

class HomeTheaterFacade {
    private Amplifier amplifier;
    private DVDPlayer dvdPlayer;
    private Projector projector;

    public HomeTheaterFacade(Amplifier amp, DVDPlayer dvd, Projector proj) {
        this.amplifier = amp;
        this.dvdPlayer = dvd;
        this.projector = proj;
    }

    public void watchMovie(String movie) {
        projector.on();
        amplifier.on();
        dvdPlayer.on();
        dvdPlayer.play(movie);
    }

    public void endMovie() {
        dvdPlayer.off();
        amplifier.off();
        projector.off();
    }
}

// Client code
public class HomeTheaterTestDrive {
    public static void main(String[] args) {
        Amplifier amp = new Amplifier();
        DVDPlayer dvd = new DVDPlayer();
        Projector proj = new Projector();
        
        HomeTheaterFacade homeTheater = new HomeTheaterFacade(amp, dvd, proj);
        homeTheater.watchMovie("Inception");
        homeTheater.endMovie();
    }

4. Best Practices

Use Facade when you want to provide a simple interface to a complex subsystem.
Consider the Facade as a single point of access to a system's functionality.
Keep the Facade interface minimal, exposing only the necessary functionality.

5. FAQ

What is the main benefit of using the Facade Pattern?

The main benefit is simplicity; it reduces the complexity of interactions with the subsystem by providing a single unified interface.

Can the Facade Pattern prevent direct access to subsystem classes?

No, it does not prevent access; it simply provides a simplified way to use them.