结构型模式：12-享元模式

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

    public void display() {
        System.out.println("棋子颜色：" + this.getColor());
    }
}

//黑色棋子类：具体享元类
class BlackIgoChessman extends IgoChessman {
    public String getColor() {
        return "黑色";
    }
}

//白色棋子类：具体享元类
class WhiteIgoChessman extends IgoChessman {
    public String getColor() {
        return "白色";
    }
}

//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);
    }
}

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
        black1.display();
        black2.display();
        black3.display();
        white1.display();
        white2.display();
    }
}

带外部状态的解决方案

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单纯享元模式

在单纯享元模式中，所有的具体享元类都是可以共享的，不存在非共享具体享元类。

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复合享元模式

复合享元对象本身不能共享，但是它们可以分解成单纯享元对象

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