享元模式

Posted 2020-12-12 diameter

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名称：

享元模式（Flyweight Pattern）

问题：

The flyweight design pattern enables use sharing of objects to support large numbers of fine-grained objects efficiently.

解决方案：

1、模式的参与者

1、Flyweight

-描述一个接口，通过这个接口flyweight可以接受并作用于外部状态。

2、ConcreteFlyweight

-实现Flyweight接口，并为内部状态（如果有的话）增加存储空间。ConcreteFlyweight对象必须是可共享的。它所存储的状态必须是内部的；即，它必须独立于ConcreteFlyweight对象的场景。

3、UnsharedConcreteFlyweight

-并非所有的Flyweight子类都需要被共享。Flyweight接口使共享成为可能，但它并不强制共享。在Flyweight对象结构的某些层次，UnsharedConcreteFlyweight对象通常将ConcreteFlyweight对象作为子节点。

4、FlyweightFactory

-创建并管理flyweight对象。

-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。

5、Client

-维持一个对flyweight的引用。

-计算或者存储一个（多个）flyweight的外部状态。

2.实现方式

class UnsharedConcreteFlyweight
{
    private String sharedInfo;
    UnsharedConcreteFlyweight(String sharedInfo)
    {
        this.sharedInfo= sharedInfo;
    }
    public String getSharedInfo()
    {
        return sharedInfo;
    }
    public void setSharedInfo(String sharedInfo)
    {
        this.sharedInfo=sharedInfo;
    }
}

interface Flyweight
{
    public void operation(UnsharedConcreteFlyweight state);
}

class ConcreteFlyweight implements Flyweight
{
    private String key;
    ConcreteFlyweight(String key)
    {
        this.key=key;
        
    }
    public void operation(UnsharedConcreteFlyweight outState)
    {
       outState.getSharedInfo()
    }
}

class FlyweightFactory
{
    private HashMap<String, Flyweight> flyweights=new HashMap<String, Flyweight>();
    public Flyweight getFlyweight(String key)
    {
        Flyweight flyweight=(Flyweight)flyweights.get(key);
        if(flyweight!=null)
        {
            System.out.println(key+" is exist!");
        }
        else
        {
            flyweight=new ConcreteFlyweight(key);
            flyweights.put(key, flyweight);
        }
        return flyweight;
    }
}