Facade

The Facade design pattern is a structural pattern that provides a simplified interface to a complex subsystem. It hides the complexities of the system and provides an easy-to-use interface for the client.

Imagine you have a complex system with many classes and subsystems. The Facade pattern allows you to create a simple interface that clients can use to interact with the system without having to know the details of how it works.

Key Concepts

1. Facade: The simplified interface that clients use to interact with the subsystem.

2. Subsystem: The complex system that the Facade simplifies.

UML Diagram

+---------+        +-----------------+
|  Client | -----> |     Facade      |
+---------+        +-----------------+
                        /   |   \
                       /    |    \
                      /     |     \
                     /      |      \
                    /       |       \
                   /        |        \
    +---------------+ +-----------+ +-----------------+
    |  Subsystem1   | |Subsystem2 | |  Subsystem3     |
    +---------------+ +-----------+ +-----------------+

--- Java Example ---

 // Subsystem classes
 public class Subsystem1 {
     public void operation1() {
         System.out.println("Subsystem1: operation1");
     }
 }

 public class Subsystem2 {
     public void operation2() {
         System.out.println("Subsystem2: operation2");
     }
 }

 public class Subsystem3 {
     public void operation3() {
         System.out.println("Subsystem3: operation3");
     }
 }

 // Facade class
 public class Facade {
     private Subsystem1 subsystem1;
     private Subsystem2 subsystem2;
     private Subsystem3 subsystem3;

     public Facade() {
         this.subsystem1 = new Subsystem1();
         this.subsystem2 = new Subsystem2();
         this.subsystem3 = new Subsystem3();
     }

     public void operation() {
         subsystem1.operation1();
         subsystem2.operation2();
         subsystem3.operation3();
     }
 }

 // Client code
 public class Client {
     public static void main(String[] args) {
         Facade facade = new Facade();
         facade.operation();
     }
 }

--- Python Example ---

 from typing import Protocol

 # Subsystem classes
 class Subsystem1:
     def operation1(self) -> None:
         print("Subsystem1: operation1")

 class Subsystem2:
     def operation2(self) -> None:
         print("Subsystem2: operation2")

 class Subsystem3:
     def operation3(self) -> None:
         print("Subsystem3: operation3")

 # Facade class
 class Facade:
     def __init__(self) -> None:
         self._subsystem1 = Subsystem1()
         self._subsystem2 = Subsystem2()
         self._subsystem3 = Subsystem3()

     def operation(self) -> None:
         self._subsystem1.operation1()
         self._subsystem2.operation2()
         self._subsystem3.operation3()

 # Client code
 if __name__ == "__main__":
     facade = Facade()
     facade.operation()