设计模式之享元模式(FlyWeight)

#include <iostream>
#include <string>
#include <list>
#include <vector>
using namespace std;
enum COLOR{WHITE,BLACK};

/************************************************************************/
/* 装饰模式的作用是为对象增加属性										*/
/************************************************************************/

struct PiecePos
{
	int x;
	int y;
	PiecePos(int a,int b):x(a),y(b){}
};

class Piece
{
public:
	virtual void draw(){}
};
class BlackPiece:public Piece
{
public:
	virtual void draw(){cout << " set a black piece"<<endl;}
};
class WhitePiece:public Piece
{
public:
	virtual void draw(){cout << " set a white piece"<<endl;}
};


class PieceBoard
{
public:
	PieceBoard(string balckname,string whitename):
	m_whitename(whitename),m_balckname(balckname),m_blackpiece(NULL),m_whitepiece(NULL)
	{

	}
	void SetPiece(COLOR color,PiecePos pos)
	{
		if (color == BLACK)
		{
			if (NULL == m_blackpiece)
			{
				m_blackpiece = new BlackPiece();
			}
			cout << m_balckname << " on the pos" << pos.x << " and " << pos.y;
			m_blackpiece->draw();
		}
		else
		{
			if (NULL == m_whitepiece)
			{
				m_whitepiece = new WhitePiece();
			}
			cout << m_whitename << " on the pos" << pos.x << " and " << pos.y;
			m_whitepiece->draw();
		}
		m_vecPos.push_back(pos);
	}
private:
	vector<PiecePos> m_vecPos;
	Piece *m_blackpiece;
	Piece *m_whitepiece;
	string m_balckname;
	string m_whitename;
};


int main()
{
	PieceBoard pieceboard("A","B");
	pieceboard.SetPiece(WHITE,PiecePos(4,6));	
	pieceboard.SetPiece(BLACK,PiecePos(3,5));
	pieceboard.SetPiece(WHITE,PiecePos(2,8));
	pieceboard.SetPiece(BLACK,PiecePos(1,9));
	return 0;
}

享元模式原理：所谓享元模式，是共享一些元数据对象，例如棋盘的棋子，如果我们对每个棋子建立一个对象然后组织成一个容器，则需要很多个对象。可以只建立两个对象，一个黑子对象，一个白子对象，由棋盘共享，棋盘维护一个保存棋子位置的对象。

代码如下：