Fly Weight Pattern （享元模式， 共享元数据）

Question

Analysis

Introduction

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Example

// Website.java

public abstract class Website {
    public abstract void use();
}

//ConcreteWebsite.java
public class ConcreteWebsite extends Website {
    private String type = ""; // the release type of a website

    public ConcreteWebsite(String type){
        this.type = type;
    }

    @Override
    public void use() {
        System.out.println("The release type of a website is :" + type);
    }
}

// WebsiteFactory.java

import java.util.HashMap;

public class WebsiteFactory {
    private HashMap<String, ConcreteWebsite> pool = new HashMap<String, ConcreteWebsite>();

    //根据网站的类型，返回一个网站， 如果没有，则创造一个网站并放入池中
    public Website getWebsiteCategory(String type){
        if(!pool.containsKey(type)){
            pool.put(type, new ConcreteWebsite(type));
        }
        return (Website) pool.get(type);
    }

    //get the number of category
    public int getWebSiteCount(){
        return pool.size();
    }
}

// Client.java
public class Client {
    public static void main(String[] args) {
        WebsiteFactory websiteFactory = new WebsiteFactory();
        Website news = websiteFactory.getWebsiteCategory("news");
        Website wechat = websiteFactory.getWebsiteCategory("wechat");
        Website qq = websiteFactory.getWebsiteCategory("QQ");
        news.use();
        wechat.use();
        qq.use();
        Website news2 = websiteFactory.getWebsiteCategory("news");
        news2.use();
        System.out.println(websiteFactory.getWebSiteCount());
    }
}
//
//        The release type of a website is :wechat
//        The release type of a website is :QQ
//        The release type of a website is :news
//        3