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  • 从代码看设计模式之----工厂模式(C++)

    设计模式依照本人理解,就是真对一类问题一个更好的标准的解决方案,按照这个解决方案做出来的东西,后续方便扩展,方便维护,等等一系列方便。不按照这个方案行不行?当然也可以,杀猪杀屁股,各有各的杀法。这是我对设计模式的两点认识:第一,设计模式只是针对一类问题较好的一个解决方案,不唯一,不一定最好;第二,不按照设计模式也能解决问题。

    遵照这个思想,我从四人帮的设计模式的书中扣了一些代码出来,调试通过,想以此让自己对设计模式的理解更为深入。毕竟四人帮书中的描述虽然经典,但是终归是没有看代码来的直接点。

    下面就来看代码。首先,要看一下没有进行过优化的代码,这个代码是打算建立一个迷宫(Maze),迷宫的元素是墙、房间、门。它们都是MapSite的子类。同时一个房间有四个方向,有可能是墙也有可能是门。

    #include <iostream>
     
    using namespace std;
     
    enum Direction {
      North,
      East,
      South,
      West,
    };
     
    class MapSite {
    public:
      virtual void Enter() = 0;
    };
     
    class Room : public MapSite {
    public:
      Room(int roomNo):_roomNumber(roomNo) {};
       
      MapSite *GetSide(Direction) const;
     
      virtual void SetSide(Direction direction, MapSite *) {
        cout << "Set the "
             << _roomNumber
             << " room "
             << direction
             << " side."
             << endl;
      };
     
      int GetRoomNo() {
        return _roomNumber;
      };
     
      virtual void Enter() {
        cout << "Enter the Room." << endl;
      };
       
    private:
      MapSite *_sides[4];
      int _roomNumber;
    };
     
    class Wall : public MapSite {
    public:
      Wall() {};
     
      virtual void Enter() {
        cout << "Enter the wall." << endl;
      };
     
    };
     
    class Door : public MapSite {
    public:
      Door(Room* = 0, Room* = 0) {};
       
      virtual void Enter() {
        cout << "Enter the door." << endl;
      };
      Room *OtherSideFrom(Room*) {};
     
    private:
      Room *_room1;
      Room *_room2;
      bool _isOpen;
    };
     
    class Maze {
    public:
      Maze() {};
     
      void AddRoom(Room* room) {
        cout << "Add the room" << room->GetRoomNo() << "." << endl;
      };
      Room* RoomNo(int) const{};
    };
     
     
    class MazeGame {
    public:
      Maze *CreateMaze();
    };
     
    Maze* MazeGame::CreateMaze() {
      Maze* aMaze = new Maze;
      Room* r1 = new Room(1);
      Room* r2 = new Room(2);
      Door* theDoor = new Door(r1, r2);
       
      aMaze->AddRoom(r1);
      aMaze->AddRoom(r2);
       
      r1->SetSide(North, new Wall);
      r1->SetSide(East, theDoor);
      r1->SetSide(South, new Wall);
      r1->SetSide(West, new Wall);
       
      r2->SetSide(North, new Wall);
      r2->SetSide(East, new Wall);
      r2->SetSide(South, new Wall);
      r2->SetSide(West, theDoor);
       
      return aMaze;
    }
     
    int main() {
      MazeGame mygame;
      mygame.CreateMaze();
      return 0;
    }

    这个源码就是普通的实现方式。按照工厂模式进行修改之后的代码如下:

    #include <iostream>
     
    using namespace std;
     
    enum Direction {
      North,
      East,
      South,
      West,
    };
     
    class MapSite {
    public:
      virtual void Enter() = 0;
    };
     
    class Room : public MapSite {
    public:
      Room(int roomNo):_roomNumber(roomNo) {};
       
      MapSite *GetSide(Direction) const;
     
      virtual void SetSide(Direction direction, MapSite *) {
        cout << "Set the "
             << _roomNumber
             << " room "
             << direction
             << " side."
             << endl;
      };
     
      int GetRoomNo() {
        return _roomNumber;
      };
     
      virtual void Enter() {
        cout << "Enter the Room." << endl;
      };
       
    private:
      MapSite *_sides[4];
      int _roomNumber;
    };
     
    class Wall : public MapSite {
    public:
      Wall() {};
     
      virtual void Enter() {
        cout << "Enter the wall." << endl;
      };
     
    };
     
    class Door : public MapSite {
    public:
      Door(Room* = 0, Room* = 0) {};
       
      virtual void Enter() {
        cout << "Enter the door." << endl;
      };
      Room *OtherSideFrom(Room*) {};
     
    private:
      Room *_room1;
      Room *_room2;
      bool _isOpen;
    };
     
    class Maze {
    public:
      Maze() {};
     
      void AddRoom(Room* room) {
        cout << "Add the room" << room->GetRoomNo() << "." << endl;
      };
      Room* RoomNo(int) const{};
    };
     
    class MazeFactory {
    public:
      MazeFactory() {};
     
      virtual Maze* MakeMaze() const {
        return new Maze;
      };
     
      virtual Wall* MakeWall() const {
        return new Wall;
      };
     
      virtual Room* MakeRoom(int n) const {
        return new Room(n);
      };
     
      virtual Door* MakeDoor(Room* r1, Room* r2) const {
        return new Door(r1, r2);
      };
    };
     
    class MazeGame {
    public:
    Maze* CreateMaze(MazeFactory &factory) {
      Maze* aMaze = factory.MakeMaze();
      Room* r1 = factory.MakeRoom(1);
      Room* r2 = factory.MakeRoom(2);
      Door* theDoor = factory.MakeDoor(r1, r2);
       
      aMaze->AddRoom(r1);
      aMaze->AddRoom(r2);
       
      r1->SetSide(North, factory.MakeWall());
      r1->SetSide(East, theDoor);
      r1->SetSide(South, factory.MakeWall());
      r1->SetSide(West, factory.MakeWall());
       
      r2->SetSide(North, factory.MakeWall());
      r2->SetSide(East, factory.MakeWall());
      r2->SetSide(South, factory.MakeWall());
      r2->SetSide(West, theDoor);
       
      return aMaze;
    };
    };
     
    int main() {
      MazeGame mygame;
      MazeFactory factory;
      mygame.CreateMaze(factory);
      return 0;
    }

    对比这两个源码就会发现,实现的功能是完全相同的,只不过第二种实现采用了工厂模式。设计模式既然好,肯定有它的好处,那我们接下来看看,如果是对这个程序进行扩展,要修改迷宫为房间里可以有炸弹的迷宫的时候,我们在采用了工厂模式之后,需要进行哪些修改。

    #include <iostream>

    using namespace std;

    enum Direction {
      North,
      East,
      South,
      West,
    };

    class MapSite {
    public:
      virtual void Enter() = 0;
    };

    class Room : public MapSite {
    public:
      Room(int roomNo):_roomNumber(roomNo) {};
     
      MapSite *GetSide(Direction) const;

      virtual void SetSide(Direction direction, MapSite *) {
        cout << "Set the "
             << _roomNumber
             << " room "
             << direction
             << " side."
             << endl;
      };

      int GetRoomNo() {
        return _roomNumber;
      };

      virtual void Enter() {
        cout << "Enter the Room." << endl;
      };
     
    private:
      MapSite *_sides[4];
      int _roomNumber;
    };

    class BombRoom : public Room {
    public:
      BombRoom(int num):Room(num) {
        _roomNum = num;
      };
      virtual void SetSide(Direction direction, MapSite *) {
        cout << "Set the "
             << _roomNum
             << " bomb room "
             << direction
             << " side."
             << endl;
      };
    private:
      int _roomNum;
    };

    class Wall : public MapSite {
    public:
      Wall() {};

      virtual void Enter() {
        cout << "Enter the wall." << endl;
      };

    };

    class Door : public MapSite {
    public:
      Door(Room* = 0, Room* = 0) {};
     
      virtual void Enter() {
        cout << "Enter the door." << endl;
      };
      Room *OtherSideFrom(Room*) {};

    private:
      Room *_room1;
      Room *_room2;
      bool _isOpen;
    };

    class Maze {
    public:
      Maze() {};

      void AddRoom(Room* room) {
        cout << "Add the room" << room->GetRoomNo() << "." << endl;
      };
      Room* RoomNo(int) const{};
    };

    class MazeFactory {
    public:
      MazeFactory() {};

      virtual Maze* MakeMaze() const {
        return new Maze;
      };

      virtual Wall* MakeWall() const {
        return new Wall;
      };

      virtual Room* MakeRoom(int n) const {
        return new Room(n);
      };

      virtual Door* MakeDoor(Room* r1, Room* r2) const {
        return new Door(r1, r2);
      };
    };

    class BombMazeFactory : public MazeFactory {
    public:
      virtual Room* MakeRoom(int n) const {
        return new BombRoom(n);
      };
    };

    class MazeGame {
    public:
    Maze* CreateMaze(MazeFactory &factory) {
      Maze* aMaze = factory.MakeMaze();
      Room* r1 = factory.MakeRoom(1);
      Room* r2 = factory.MakeRoom(2);
      Door* theDoor = factory.MakeDoor(r1, r2);
     
      aMaze->AddRoom(r1);
      aMaze->AddRoom(r2);
     
      r1->SetSide(North, factory.MakeWall());
      r1->SetSide(East, theDoor);
      r1->SetSide(South, factory.MakeWall());
      r1->SetSide(West, factory.MakeWall());
     
      r2->SetSide(North, factory.MakeWall());
      r2->SetSide(East, factory.MakeWall());
      r2->SetSide(South, factory.MakeWall());
      r2->SetSide(West, theDoor);
     
      return aMaze;
    };
    };

    int main() {
      MazeGame mygame;
    //  MazeFactory factory;
      BombMazeFactory factory;
      mygame.CreateMaze(factory);
      return 0;
    }

    可以看出改动量很小,而且可以随时把代码改回原来的生成普通迷宫的情况。如果是在最初没有采用工厂模式的代码上进行修改呢?那工作量是显而易见的了,有兴趣的可以自己试试,在这里不再累述。

    后续会继续分析工厂方法模式。

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  • 原文地址:https://www.cnblogs.com/ainima/p/6331966.html
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