外觀模式

外觀模式（Facade pattern），是軟件工程中常用的一種軟件設計模式，它為子系統中的一組接口提供一個統一的高層接口，使得子系統更容易使用。

結構

Facade

這個外觀類為子系統中Packages 1、2、3提供一個共同的對外接口

Clients

客戶對象通過一個外觀接口讀寫子系統中各接口的數據資源。

Packages

客戶可以通過外觀接口讀取的内部庫。

示例

Java

這是一個抽象的示例。一個客戶“you”通過外觀接口“computer”獲取計算機内部複雜的系統信息。

/* Complex parts */
 
class CPU {
        public void freeze() { ... }
        public void jump(long position) { ... }
        public void execute() { ... }
}
 
class Memory {
        public void load(long position, byte[] data) {
                ...
        }
}
 
class HardDrive {
        public byte[] read(long lba, int size) {
                ...
        }
}
 
/* Façade */
 
class Computer {
        public void startComputer() {
                cpu.freeze();
                memory.load(BOOT_ADDRESS, hardDrive.read(BOOT_SECTOR, SECTOR_SIZE));
                cpu.jump(BOOT_ADDRESS);
                cpu.execute();
        }
}
 
/* Client */
 
class You {
        public static void main(String[] args) {
                Computer facade = new Computer();
                facade.startComputer();
        }
}

C#

// Facade pattern -- Structural example 
 
using System;
 
namespace DoFactory.GangOfFour.Facade.Structural
{
 
  // Mainapp test application 
 
  class MainApp
  {
    public static void Main()
    {
      Facade facade = new Facade();
 
      facade.MethodA();
      facade.MethodB();
 
      // Wait for user 
      Console.Read();
    }
  }
 
  // "Subsystem ClassA" 
 
  class SubSystemOne
  {
    public void MethodOne()
    {
      Console.WriteLine(" SubSystemOne Method");
    }
  }
 
  // Subsystem ClassB" 
 
  class SubSystemTwo
  {
    public void MethodTwo()
    {
      Console.WriteLine(" SubSystemTwo Method");
    }
  }
 
  // Subsystem ClassC" 
 
  class SubSystemThree
  {
    public void MethodThree()
    {
      Console.WriteLine(" SubSystemThree Method");
    }
  }
 
  // Subsystem ClassD" 
 
  class SubSystemFour
  {
    public void MethodFour()
    {
      Console.WriteLine(" SubSystemFour Method");
    }
  }
 
  // "Facade" 
 
  class Facade
  {
    SubSystemOne one;
    SubSystemTwo two;
    SubSystemThree three;
    SubSystemFour four;
 
    public Facade()
    {
      one = new SubSystemOne();
      two = new SubSystemTwo();
      three = new SubSystemThree();
      four = new SubSystemFour();
    }
 
    public void MethodA()
    {
      Console.WriteLine("\nMethodA() ---- ");
      one.MethodOne();
      two.MethodTwo();
      four.MethodFour();
    }
 
    public void MethodB()
    {
      Console.WriteLine("\nMethodB() ---- ");
      two.MethodTwo();
      three.MethodThree();
    }
  }
}

C++

class CPU {
public:
        void freeze() { ... }
        void jump(long position) { ... }
        void execute() { ... }
}
 
class Memory {
public:
        void load(long position, char* data) {
                ...
        }
}
 
class HardDrive {
public:
        char* read(long lba, int size) {
                ...
        }
}
 
/* Façade */
 
class Computer {
public:
        void startComputer() {
                cpu.freeze();
                memory.load(BOOT_ADDRESS, hardDrive.read(BOOT_SECTOR, SECTOR_SIZE));
                cpu.jump(BOOT_ADDRESS);
                cpu.execute();
        }
}
 
/* Client */
 
class You {
public:
        void start(String[] args) {
                Computer facade = new Computer();
                facade.startComputer();
        }
}