浅析设计模式之享元设计模式

Posted 2021-04-25 Dszmr

享元模式的定义与特点

享元（Flyweight）模式的定义：运用共享技术来有効地支持大量细粒度对象的复用。它通过共享已经存在的又像来大幅度减少需要创建的对象数量、避免大量相似类的开销，从而提高系统资源的利用率。

享元模式的主要优点是：相同对象只要保存一份，这降低了系统中对象的数量，从而降低了系统中细粒度对象给内存带来的压力。

其主要缺点是：

1. 为了使对象可以共享，需要将一些不能共享的状态外部化，这将增加程序的复杂性。

2. 读取享元模式的外部状态会使得运行时间稍微变长。

代码实现

package cn.dszmr.sjms.xyms;

/**
 * 实体对象
 */
public class UnsharedConcreteFlyweight {
    private String key;

    public UnsharedConcreteFlyweight(String key) {
        this.key = key;
    }

    public String getKey() {
        return key;
    }

    public void setKey(String key) {
        this.key = key;
    }
}

package cn.dszmr.sjms.xyms;

/**
 * 享元接口
 */
public interface Flyweight {
    void operation(UnsharedConcreteFlyweight state);
}

package cn.dszmr.sjms.xyms;

/**
 * 具体享元类
 */
public class ConcreteFlyweight implements Flyweight {
    private String key;

    public ConcreteFlyweight(String key) {
        this.key = key;
        System.out.println("key被创建");
    }

    @Override
    public void operation(UnsharedConcreteFlyweight state) {
        System.out.print("具体享元"+key+"被调用，");
        System.out.println("非享元信息是:"+state.getKey());
    }
}

package cn.dszmr.sjms.xyms;

import java.util.HashMap;

/**
 * 享元工厂
 */
public class FlyweightFactory {
    private HashMap<String,Flyweight>  flyweights = new HashMap<>();
    public Flyweight getFlyweight(String key){
        Flyweight flyweight = flyweights.get(key);

        if (flyweight != null){
            System.out.println(key+"已存在并且被成功获取！");
        }else {
            flyweight = new ConcreteFlyweight(key);
            flyweights.put(key,flyweight);
        }
        return flyweight;
    }
}

package cn.dszmr.sjms.xyms;

/**
 * 测试类
 */
public class FlyweightPattern
{
    public static void main(String[] args)
    {
        FlyweightFactory factory=new FlyweightFactory();
        Flyweight f01=factory.getFlyweight("a");
        Flyweight f02=factory.getFlyweight("a");
        Flyweight f03=factory.getFlyweight("a");
        Flyweight f11=factory.getFlyweight("b");
        Flyweight f12=factory.getFlyweight("b");
        f01.operation(new UnsharedConcreteFlyweight("第1次调用a。"));
        f02.operation(new UnsharedConcreteFlyweight("第2次调用a。"));
        f03.operation(new UnsharedConcreteFlyweight("第3次调用a。"));
        f11.operation(new UnsharedConcreteFlyweight("第1次调用b。"));
        f12.operation(new UnsharedConcreteFlyweight("第2次调用b。"));
    }
}