享元模式 FlyWeight

c++ 享元模式(flyweight)

例子(大话设计模式上的例子 c++的):

// FlyWeight.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"


#include <IOSTREAM>
#include <STRING>
#include   <map> 
using namespace std;

////////////////////////////////////////
//version 1
class website1{
public:
    website1(string name):m_name(name){}
    void show(){
        cout<<this->m_name<<endl;
    }

private:
    string m_name;
};
/////////////////////////////////////////
//version 2
//实现了共享对象,但是数据都是相同的
class website2{
public:
    virtual void show() = 0;
};

class concretewebsite2:public website2{
public:
    concretewebsite2(string name):m_name(name){}
    void show(){
        cout<<this->m_name<<endl;
    }
private:
    string m_name;
};

class website2factory{
public:
    concretewebsite2 * getwebsite(string type){
        map<string,concretewebsite2 *>::iterator it ;
        it = m_map.find(type);
        if(it == m_map.end())
            //    m_map.insert(pair<string , concretewebsite *>(type,new concretewebsite(type)));
                m_map[type] = new concretewebsite2(type);
        return m_map[type];
    }
    int getwebsitecount(){
        return m_map.size();
    }
private:
    map<string ,concretewebsite2 * > m_map;
};

//////////////////////////////////////
//version 3
class User{
public:
    User(string name):m_username(name){}
    string getusername() const{
        return m_username;
    }
private:
    string m_username;
};

class website3{
public:
    virtual void show(const User & user) = 0;      //将数据分离开来,但内部处理还是同一对象
};

class concretewebsite3:public website3{
public:
    concretewebsite3(string name):m_name(name){}
    void show( const User & user){                     
        cout<<this->m_name<<"   "<<user.getusername()<<endl;
    }
private:
    string m_name;
};

class website3factory{
public:
    concretewebsite3 * getwebsite(string type){
        map<string,concretewebsite3 * >::iterator it;
        it = m_map.find(type);
        if(it == m_map.end()){
            m_map[type] = new concretewebsite3(type);
        }
        return m_map[type];
    }

    int getwebsitecount(){
        return m_map.size();
    }
private:
    map<string,concretewebsite3 * > m_map;
};
int main(int argc, char* argv[])
{
    // version 1 ,浪费对象
    //     website1 *p1 = new website1("movie");
    //     website1 *p2 = new website1("blog");
    //     website1 *p3 = new website1("music");
    //     p1->show();
    //     p2->show();
    //     p3->show();

    // version 2,共享了对象,但是数据还都是相同的,还需修改
    //     website2factory * fac = new website2factory;
    //     website2 * p1 = fac->getwebsite("blog");
    //     website2 * p2 = fac->getwebsite("blog");
    //     p1->show();
    //     p2->show();
    //     cout<<fac->getwebsitecount()<<endl;

    //version 3,将user身份传递给给website的show函数,就是对共享的对象,分不同的身份,即实现了数据分离
    website3factory * fac = new website3factory;
    website3 * p1 = fac->getwebsite("blog");
    website3 * p2 = fac->getwebsite("blog");
    cout<<"the website count is "<<fac->getwebsitecount()<<endl;  //只有一个“blog”website产生,
    website3 * p3 = fac->getwebsite("movie");
    website3 * p4 = fac->getwebsite("music");
    cout<<"the website count is "<<fac->getwebsitecount()<<endl;  // 1个“blog” 1个“movie” 1个“music”
    User user1("xiaowang");
    User user2("xiaohong");
    User user3("xiaohei");
    User user4("xiaogang");
    p1->show(user1);
    p2->show(user2);
    p3->show(user3);
    p4->show(user4);
    
    return 0;
}

 

 

举个围棋的例子,围棋的棋盘共有361格,即可放361个棋子。现在要实现一个围棋程 序,该怎么办呢?首先要考虑的是棋子棋盘的实现,可以定义一个棋子的类,成员变量包括棋子的颜色、形状、位置等信息,另外再定义一个棋盘的类,成员变量中 有个容器,用于存放棋子的对象。下面给出代码表示:

        棋子的定义,当然棋子的属性除了颜色和位置,还有其他的,这里略去。这两个属性足以说明问题。

 

复制代码
#include <iostream>
#include <vector>
#include <string>


enum PieceColor {BLACK,WHITE};
using namespace std;

class Pos
{
public:
    Pos(int x,int y):m_x(x),m_y(y)
    {
    
    }
    int getX()
    {
        return m_x;
    }
    int getY()
    {
        return m_y;
    }
private:
    int m_x;
    int m_y;
};

class Piece
{
public:
    Piece(PieceColor color,Pos pos):m_color(color),m_pos(pos){};
    ~Piece() {}
    virtual void Draw() {}
protected:
    PieceColor m_color;
    Pos m_pos;
    
};

class WhitePiece : public Piece
{
public:
    WhitePiece(PieceColor color, Pos pos):Piece(color,pos){}
    ~WhitePiece();
    virtual void Draw() {
        cout << "draw a white piece" << endl;
    }
};

class BlackPiece:public Piece
{
public:
    BlackPiece(PieceColor color,Pos pos):Piece(color,pos){}
    ~BlackPiece();
    virtual void Draw(){

    cout << "draw a black piece" <<endl;

    }
};

class PieceBoard
{
public:
    PieceBoard(string black,string white):m_blackName(black),m_whiteName(white)
    {
    
    }
    ~PieceBoard() {
        Clear();
    }
    void SetPiece(PieceColor color,Pos pos)
    {
        Piece * piece = NULL;
        if(color == BLACK)
        {
            piece = new BlackPiece(color,pos);
            std::cout << m_blackName << "在位置(" << pos.getX() << ","<<pos.getY() <<")" <<endl ;
            piece->Draw();
            m_pieceArray.push_back(piece);
        }
        else
        {
            piece = new WhitePiece(color,pos);
            std::cout << m_whiteName << "在位置(" << pos.getX() << ","<<pos.getY() <<")" <<endl;
            piece->Draw();
            m_pieceArray.push_back(piece);
        }
    }
    void Clear()
    {
        int size = m_pieceArray.size();
        for(int i = 0; i < size ; i++)
            delete m_pieceArray[i];
    }
private:
    std::vector<Piece*> m_pieceArray;
    std::string m_blackName;
    std::string m_whiteName;
};
复制代码

 

主函数:

复制代码
#include "flyweight.h"
int main()
{
    PieceBoard pieceBoard("A","B");
    pieceBoard.SetPiece(BLACK,Pos(4,4));
    pieceBoard.SetPiece(WHITE,Pos(16,6));

    system("pause");
    return 0;
}
复制代码

 可以发现,棋盘的容器中存放了已下的棋子,而每个棋子包含棋子的所有属性。一盘棋往往需要含上百颗棋子,采用上面这种实现,占用的空间太大了。如何改进呢?用享元模式。其定义为:运用共享技术有效地支持大量细粒度的对象。

        在围棋中,棋子就是大量细粒度的对象。其属性有内在的,比如颜色、形 状等,也有外在的,比如在棋盘上的位置。内在的属性是可以共享的,区分在于外在属性。因此,可以这样设计,只需定义两个棋子的对象,一颗黑棋和一颗白棋, 这两个对象含棋子的内在属性;棋子的外在属性,即在棋盘上的位置可以提取出来,存放在单独的容器中。相比之前的方案,现在容器中仅仅存放了位置属性,而原 来则是棋子对象。显然,现在的方案大大减少了对于空间的需求。

       关注PieceBoard 的容器,之前是vector<Piece*> m_vecPiece,现在是vector<PiecePos> m_vecPos。这里是关键。

       棋子的新定义,只包含内在属性:

 

复制代码
#include <iostream>
#include <vector>
#include <string>


enum PieceColor {BLACK,WHITE};
using namespace std;

class Pos
{
public:
    Pos(int x,int y):m_x(x),m_y(y)
    {
    
    }
    int getX()
    {
        return m_x;
    }
    int getY()
    {
        return m_y;
    }
private:
    int m_x;
    int m_y;
};

class Piece
{
public:
    Piece(PieceColor color):m_color(color){};
    ~Piece() {}
    virtual void Draw() {}
protected:
    PieceColor m_color;
    
};

class WhitePiece : public Piece
{
public:
    WhitePiece(PieceColor color):Piece(color){}
    ~WhitePiece();
    virtual void Draw() {
        cout << "draw a white piece" << endl;
    }
};

class BlackPiece:public Piece
{
public:
    BlackPiece(PieceColor color):Piece(color){}
    ~BlackPiece();
    virtual void Draw(){

    cout << "draw a black piece" <<endl;

    }
};

class PieceBoard
{
public:
    PieceBoard(string black,string white):m_blackName(black),m_whiteName(white)
    {
    
    }
    ~PieceBoard() {
        Clear();
    }
    void SetPiece(PieceColor color,Pos pos)
    {
        Piece * piece = NULL;
        if(color == BLACK)
        {
            piece = new BlackPiece(color);
            std::cout << m_blackName << "在位置(" << pos.getX() << ","<<pos.getY() <<")" <<endl ;
            piece->Draw();
            m_blackPosArray.push_back(pos);
        }
        else
        {
            piece = new WhitePiece(color);
            std::cout << m_whiteName << "在位置(" << pos.getX() << ","<<pos.getY() <<")" <<endl;
            piece->Draw();
            m_whitePosArray.push_back(pos);
        }
    }
    void Clear()
    {
        //int size = m_pieceArray.size();
        //for(int i = 0; i < size ; i++)
        //    delete m_pieceArray[i];
    }
private:
    std::vector<Pos> m_whitePosArray;
    std::vector<Pos> m_blackPosArray;
    std::string m_blackName;
    std::string m_whiteName;
};
复制代码

 

主函数:

复制代码
#include "flyweight.h"
int main()
{
    PieceBoard pieceBoard("A","B");
    pieceBoard.SetPiece(BLACK,Pos(4,4));
    pieceBoard.SetPiece(WHITE,Pos(16,6));

    system("pause");
    return 0;
}
 
转载自:http://www.cnblogs.com/onlycxue/p/3487863.html
posted @ 2015-07-10 20:19  朽木可雕否  阅读(133)  评论(0编辑  收藏  举报