17 结构型模式-享元模式

1 享元模式介绍

2 享元模式原理

3 享元模式实现

抽象享元类可以是一个接口也可以是一个抽象类,作为所有享元类的公共父类, 主要作用是提高系统的可扩展性.

//* 抽象享元类
public abstract class Flyweight {public abstract void operation(String extrinsicState);
}

具体享元类
具体享元类中要将内部状态和外部状态分开处理,内部状态作为具体享元类的成员变量,而外部状态通过注入的方式添加到具体享元类中.

/*** 可共享的-具体享元类* 注意: 在具体享元类中,需要将内部状态和外部状态分开处理.**/
public class ConcreteFlyweight extends Flyweight{//内部状态 : inState作为一个成员变量,同一个享元对象的内部状态是一致的.private String inState;public ConcreteFlyweight(String inState) {this.inState = inState;}/*** 外部状态在使用的时候,通常是有外部设置,不保存在享元对象中,即使是同一个对象* @param state*/@Overridepublic void operation(String state) {System.out.println("=== 享元对象的内部状态: " + inState + ",外部状态: " + state );}
}

非共享享元类,不复用享元工厂内部状态,但是是抽象享元类的子类或实现类

/*** 非共享的具体享元类**/
public class UnsharedFlyweight  extends Flyweight{private String inState;public UnsharedFlyweight(String inState) {this.inState = inState;}@Overridepublic void operation(String state) {System.out.println("=== 使用不共享对象,内部状态: " + inState + ",外部状态: " + state );}
}

享元工厂类, 管理一个享元对象类的缓存池。它会存储享元对象之间需要传递的共有状态，比如，按照大写英文字母来作为状态标识，这种只在享元对象之间传递的方式就叫内部状态。同时，它还提供了一个通用方法getFlyweight()，主要通过内部状态标识来获取享元对象。

/*** 享元工厂类* 作用: 作为存储享元对象的享元池.用户获取享元对象时先从享元池中获取,有则返回,没有创建新的返回给用户,* 并且在享元池中保存**/
public class FlyweightFactory {//定义一个Map集合用于存储享元对象,实现享元池private Map<String,Flyweight> pool = new HashMap<>();//实现享元对象之间的状态传递public FlyweightFactory() {//添加对应的内部状态pool.put("A",new ConcreteFlyweight("A"));pool.put("B",new ConcreteFlyweight("B"));pool.put("C",new ConcreteFlyweight("C"));}//根据内部状态进行查找public Flyweight getFlyweight(String key){//对象是否存在if(pool.containsKey(key)){System.out.println("=== 享元池中存在,直接复用,key : " + key);return pool.get(key);}else{//如果对象不存在,就创建一个添加到享元池,然后返回System.out.println("=== 享元池中不存在,创建并复用,key: " + key);Flyweight fw = new ConcreteFlyweight(key);pool.put(key,fw);return  fw;}}
}

public class Client {public static void main(String[] args) {//获取工厂对象FlyweightFactory factory = new FlyweightFactory();//通过工厂对象获取共享的享元对象Flyweight a1 = factory.getFlyweight("A");a1.operation("a1ExState");Flyweight a2 = factory.getFlyweight("A");a2.operation("a2ExState");System.out.println(a1 == a2);//获取非共享的享元对象UnsharedFlyweight u1 = new UnsharedFlyweight("A");UnsharedFlyweight u2 = new UnsharedFlyweight("A");System.out.println(u1 == u2);}
}

4 享元模式应用实例

/*** 抽象享元类: 五子棋**/
public abstract class GobangFlyweight {public abstract String getColor();public void display(){System.out.println("棋子颜色: " + this.getColor());}
}

/*** 共享享元类-白色棋子**/
public class WriteGobang extends GobangFlyweight {@Overridepublic String getColor() {return "白色";}
}

/*** 共享享元类-黑色棋子**/
public class BlackGobang extends GobangFlyweight {@Overridepublic String getColor() {return "黑色";}
}

/*** 享元工厂类-生产五子棋棋子**/
public class GobangFactory {//享元池private static Map<String,GobangFlyweight> pool;//创建共享享元对象,设置对象的内部状态private GobangFactory() {pool = new HashMap<>();GobangFlyweight black = new BlackGobang(); //黑子GobangFlyweight write = new WriteGobang(); //白子pool.put("b",black);pool.put("w",write);}//获取唯一享元工厂对象的方法public static GobangFactory getInstance(){return SingletonHolder.INSTANCE;}//静态内部类private static class SingletonHolder{private static final GobangFactory INSTANCE = new GobangFactory();}//通过key获取集合中的享元对象public GobangFlyweight getGobang(String key){return pool.get(key);}}

public class Client {public static void main(String[] args) {GobangFactory instance = GobangFactory.getInstance();//获取3颗黑子GobangFlyweight b1 = instance.getGobang("b");GobangFlyweight b2 = instance.getGobang("b");GobangFlyweight b3 = instance.getGobang("b");System.out.println("判断黑子是否是同一对象: " + (b1 == b2));GobangFlyweight w1 = instance.getGobang("w");GobangFlyweight w2 = instance.getGobang("w");System.out.println("判断白子是否是同一对象: " + (w1 == w2));//显示棋子b1.display();b2.display();b3.display();w1.display();w2.display();}
}

5 享元模式总结