设计模式完结（11）-- 享元模式---实现对象的复用

class FlyweightFactory {
    //定义一个HashMap用于存储享元对象，实现享元池
       private HashMap flyweights = newHashMap();

       public Flyweight getFlyweight(String key){
              //如果对象存在，则直接从享元池获取
              if(flyweights.containsKey(key)){
                     return(Flyweight)flyweights.get(key);
              }
              //如果对象不存在，先创建一个新的对象添加到享元池中，然后返回
              else {
                     Flyweight fw = newConcreteFlyweight();
                     flyweights.put(key,fw);
                     return fw;
              }
       }
}

class Flyweight {
     //内部状态intrinsicState作为成员变量，同一个享元对象其内部状态是一致的
       private String intrinsicState;

       public  Flyweight(String intrinsicState) {
              this.intrinsicState=intrinsicState;
       }
　　
        //**********外部状态extrinsicState在使用时由外部设置，不保存在享元对象中，即使是同一个对象，在每一次调用时也可以传入不同的外部状态
       public void operation(String  extrinsicState) {
              ......
       }     
}

//围棋棋子工厂类：享元工厂类，使用单例模式进行设计  
class IgoChessmanFactory {  
    private static IgoChessmanFactory instance = new IgoChessmanFactory();  
    private static Hashtable ht; //使用Hashtable来存储享元对象，充当享元池  

    private IgoChessmanFactory() {  
        ht = new Hashtable();  
        IgoChessman black,white;  
        black = new BlackIgoChessman();  
        ht.put("b",black);  
        white = new WhiteIgoChessman();  
        ht.put("w",white);  
    }  

    //返回享元工厂类的唯一实例  
    public static IgoChessmanFactory getInstance() {  
        return instance;  
    }  

    //通过key来获取存储在Hashtable中的享元对象  
    public static IgoChessman getIgoChessman(String color) {  
        return (IgoChessman)ht.get(color);    
    }  
}

//坐标类：外部状态类  
class Coordinates {  
    private int x;  
    private int y;  

    public Coordinates(int x,int y) {  
        this.x = x;  
        this.y = y;  
    }  

    public int getX() {  
        return this.x;  
    }  

    public void setX(int x) {  
        this.x = x;  
    }  

    public int getY() {  
        return this.y;  
    }  

    public void setY(int y) {  
        this.y = y;  
    }  
}   

//围棋棋子类：抽象享元类  
abstract class IgoChessman {  
    public abstract String getColor();  

    public void display(Coordinates coord){  
        System.out.println("棋子颜色：" + this.getColor() + "，棋子位置：" + coord.getX() + "，" + coord.getY() );    
    }  
}
class Client {  
    public static void main(String args[]) {  
        IgoChessman black1,black2,black3,white1,white2;  
        IgoChessmanFactory factory;  

        //获取享元工厂对象  
        factory = IgoChessmanFactory.getInstance();  

        //通过享元工厂获取三颗黑子  
        black1 = factory.getIgoChessman("b");  
        black2 = factory.getIgoChessman("b");  
        black3 = factory.getIgoChessman("b");  
        System.out.println("判断两颗黑子是否相同：" + (black1==black2));  

        //通过享元工厂获取两颗白子  
        white1 = factory.getIgoChessman("w");  
        white2 = factory.getIgoChessman("w");  
        System.out.println("判断两颗白子是否相同：" + (white1==white2));  

        //显示棋子，同时设置棋子的坐标位置  
        black1.display(new Coordinates(1,2));  
        black2.display(new Coordinates(3,4));  
        black3.display(new Coordinates(1,3));  
        white1.display(new Coordinates(2,5));  
        white2.display(new Coordinates(2,4));  
    }  
}