设计模式-享元模式

用途

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享元模式 (Flyweight)

运用共享技术有效地支持大量细粒度的对象。

享元模式是一种结构型模式。

结构

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图-享元模式结构图

Flyweight : 它是所有具体享元类的超类或接口，通过这个接口，Flyweight 可以接受并作用于外部状态。

abstract class Flyweight {
    public abstract void Operation(int extrinsicstates);
}

ConcreteFlyweight :  是继承 Flyweight 超类或实现 Flyweight 接口，并为内部状态增加存储空间。

class ConcreteFlyweight extends Flyweight {
    @Override
    public void Operation(int extrinsicstates) {
        System.out.println("共享的Flyweight : " + extrinsicstates);
    }
}

UnsharedConcreteFlyweight : 指那些不需要共享的 Flyweight 子类，因为 Flyweight 接口共享成为可能，但它并不强制共享。

class UnsharedConcreteFlyweight extends Flyweight {
    @Override
    public void Operation(int extrinsicstates) {
        System.out.println("不共享的Flyweight : " + extrinsicstates);
    }
}

FlywightFactory :是一个享元工厂，用来创建并管理 Flyweight 对象。它主要是用来确保合理地共享 Flyweight ，当用户请求一个 Flyweight 时， FlyweightFactory 对象提供一个已创建的实例或创建一个（如果对象不存在的话）。

class FlywightFactory {
    private Hashtable<String, Flyweight> flyweights = new Hashtable<String, Flyweight>();
    
    public FlywightFactory() {
        flyweights.put("X", new ConcreteFlyweight());
        flyweights.put("Y", new ConcreteFlyweight());
        flyweights.put("Z", new ConcreteFlyweight());
    }
    
    public Flyweight GetFlyweight(String key) {
        return ((Flyweight)flyweights.get(key));
    }
}

测试代码

public class FlyweightPattern {
    public static void main(String[] args) {
        int extrinsicstates = 1;    
        FlywightFactory factory = new FlywightFactory();
        
        Flyweight fx = factory.GetFlyweight("X");
        fx.Operation(extrinsicstates);
        
        Flyweight fy = factory.GetFlyweight("Y");
        fy.Operation(++extrinsicstates);
        
        Flyweight fz = factory.GetFlyweight("Z");
        fz.Operation(++extrinsicstates);
        
        Flyweight uf = new UnsharedConcreteFlyweight();
        uf.Operation(++extrinsicstates);
    }
}

运行结果

共享的Flyweight : 1
共享的Flyweight : 2
共享的Flyweight : 3
不共享的Flyweight : 4