What is the Facade Pattern?
The Facade Pattern is a structural design pattern that provides a simplified interface to a complex subsystem. It hides the complexities of the system and provides a cleaner and easier-to-use API to the client.
Intent
- Provide a unified, high-level interface to a set of interfaces in a subsystem.
- Make the subsystem easier to use.
When to Use
- When you want to simplify interaction with complex systems.
- When you want to reduce dependencies between client code and subsystems.
- When refactoring large legacy systems.
Components
- Subsystem Classes – Complex classes with various functions.
- Facade Class – Wraps the subsystem and exposes only necessary functionality.
- Client – Uses the facade instead of calling subsystem classes directly.
Java Example
Imagine a Home Theater System with multiple components.
Step 1: Subsystem Classes
class Amplifier {
public void on() { System.out.println("Amplifier ON"); }
public void setVolume(int level) { System.out.println("Volume set to " + level); }
}
class DVDPlayer {
public void on() { System.out.println("DVD Player ON"); }
public void play(String movie) { System.out.println("Playing movie: " + movie); }
}
class Projector {
public void on() { System.out.println("Projector ON"); }
public void wideScreenMode() { System.out.println("Projector in widescreen mode"); }
}
Step 2: Facade Class
public class HomeTheaterFacade {
private Amplifier amp;
private DVDPlayer dvd;
private Projector projector;
public HomeTheaterFacade(Amplifier amp, DVDPlayer dvd, Projector projector) {
this.amp = amp;
this.dvd = dvd;
this.projector = projector;
}
public void watchMovie(String movie) {
System.out.println("Get ready to watch a movie...");
amp.on();
amp.setVolume(5);
projector.on();
projector.wideScreenMode();
dvd.on();
dvd.play(movie);
}
}
Step 3: Client Code
public class Main {
public static void main(String[] args) {
Amplifier amp = new Amplifier();
DVDPlayer dvd = new DVDPlayer();
Projector projector = new Projector();
HomeTheaterFacade homeTheater = new HomeTheaterFacade(amp, dvd, projector);
homeTheater.watchMovie("Inception");
}
}
Output
Get ready to watch a movie...
Amplifier ON
Volume set to 5
Projector ON
Projector in widescreen mode
DVD Player ON
Playing movie: Inception
Summary
| Aspect | Description |
|---|---|
| Pattern Type | Structural |
| Main Goal | Simplify interaction with complex systems |
| Real-Life Examples | Car dashboard, TV remote, ATM interface |
Benefits
- Simplifies client usage.
- Reduces dependency on subsystem internals.
- Promotes loose coupling.
Caution
- Facade shouldn’t become a “God Object” doing too much.
- Clients should still be able to access subsystem classes directly if needed.
This pattern is perfect when you want to decouple your code from implementation details or legacy complexity.
