# Purpose

The Facade pattern provides a unified and simplified interface to a set of interfaces in a subsystem.

It facilitates the use of large and complex systems for clients.

# Problem

The complexity associated with systems with multiple interdependent components or subsystems with their own interfaces.

These systems are difficult to understand, generate coupling, and make changes difficult.

# Solution

The solution proposed by the Facade is:

• Unified Interface: Simplifies interaction with the subsystem.

• Coupling Reduction: Clients don't need to know the inner details.

# Structure

# Participants

• Facade: Delegates requests to appropriate objects in the subsystem.
• Subsystems Class: Implements the subsystem functionality.
• Client: Accesses the subsystem through the Facade.

# When to Use It

• To provide a simple interface to a complex subsystem.

• When there are many dependencies between clients and implementation classes.

# Example: Home Theater

We are developing an integrated system consisting of TV, DVD/BluRay, Surround Sound, etc. Each one with its own interface.

# Java Code

class HomeTheaterFacade {
    private Television tv;
    private SoundSystem sound;
    private BluRayPlayer bluRay;

    public void watchMovie() {
        tv.turnOn();
        sound.turnOn();
        bluRay.turnOn();
        bluRay.play();
    }
}

public class Client {
    public static void main(String[] args) {
        HomeTheaterFacade facade = new HomeTheaterFacade(tv, sound, bluRay);
        facade.watchMovie();
    }
}

# Mapping Participants

• Television, Sound, BluRay (Subsystems): Internal classes.
• HomeTheaterFacade (Facade): Simplified interface.
• Client: Uses the Facade.

# Conclusions

The Facade pattern vastly simplifies user interaction. If we add another device, we only need to modify the Facade without affecting clients.

# Related Patterns