享元模式

享元模式（Flyweight） 运用共享技术有效地支持大量细粒度的对象

 使用场景：

如果一个应用程序使用了大量的对象，而大量的对象造成了很大的存储开销时就应该考虑使用；还有就是对象的
大多数状态可以外部状态，如果删除对象的外部状态，那么就可以用相对较少的共享对象取代很多组对象，
此时就可以考虑享元模式

使用好处：

享元模式可以避免大量非常类似的开销。再程序设计中，有时需要生成大量细粒度的类实例来表示数据。
如果发现这些实列除了几个参数外基本上都相同，有时就能够大幅度的减少需要实例化的类的数量。如果
把这些参数移到类实例的外面，在方法调用时将它们传递进来，就可以通过共享大幅度的减少单个实例的个数。

实现代码如下：

public abstract class Flyweight {
    public abstract void operation(int extrinsicstate);
}

public class ConcreteFlyweight extends Flyweight{

    @Override
    public void operation(int extrinsicstate) {
        System.out.println("具体实现Flyweight--》"+extrinsicstate);
        
    }

}

public class UnSharedConcreteFlyweight extends Flyweight{

    @Override
    public void operation(int extrinsicstate) {
        System.out.println("不共享具体实现Flyweight--》"+extrinsicstate);
        
    }

}

import com.sun.org.apache.xalan.internal.xsltc.runtime.Hashtable;

public class FlyweightFactory {
    private Hashtable flyweights = new Hashtable();

    public FlyweightFactory() {
        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);
    }
    
}

public  class FlyweightTest {
    public static void main(String[] args) {
        int extrinsicstate = 22;
        FlyweightFactory f = new FlyweightFactory();
         
        ConcreteFlyweight fx = (ConcreteFlyweight) f.getFlyweight("x");
        fx.operation(--extrinsicstate);
        
        ConcreteFlyweight fy = (ConcreteFlyweight) f.getFlyweight("y");
        fy.operation(--extrinsicstate);
        
        ConcreteFlyweight fz = (ConcreteFlyweight) f.getFlyweight("z");
        fz.operation(--extrinsicstate);
        
        UnSharedConcreteFlyweight uf = new UnSharedConcreteFlyweight();
        uf.operation(--extrinsicstate);
    }
}

具体实现Flyweight--》21
具体实现Flyweight--》20
具体实现Flyweight--》19
不共享具体实现Flyweight--》18