享元模式

    /**
     * 享元模式
     *      运用共享技术有效的支持大量细粒度的对象.
     *
     * 享元模式的内部&外部状态
     *      享元模式内部是不会随环境变化而变化的部分,可以称为是享元对象的内部状态
     *      而随着环境改变而改变,不可以共享的部分就是享元对象的外部状态了.
     *
     * 作用:
     *      享元模式可以避免大量的非常相似的类的开销.
     *
     * 应用场景:
     *      在程序设计中有时候需要生成大量细粒度的类的实例来表示数据.如果能发现这些实例除了几个
     *      参数外基本都是相同的,有时就能够大幅度的减少需要实例化的类的数量.
     *      如果能够把那些参数移到类实例的外部,在方法调用时将他们传递进来,就可以通过共享大幅度的减少单个实例的数量.
     */

结构图

范例

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

public class FlyweightFactory {
    public static String TYPE_1="com.junx.designpattem.FlyweightPattern.Demo.FlyweightFactory.1";
    public static String TYPE_2="com.junx.designpattem.FlyweightPattern.Demo.FlyweightFactory.2";
    public static String TYPE_3="com.junx.designpattem.FlyweightPattern.Demo.FlyweightFactory.3";

    static private  HashMap<String,Flyweight> map=new HashMap<>();
    static {
        map.put(TYPE_1,new ConcreteFlyweight());
        map.put(TYPE_2,new ConcreteFlyweight());
        map.put(TYPE_3,new ConcreteFlyweight());
    }

    static public Flyweight getFlyweight(String key){
        return map.get(key);
    }
}

public class ConcreteFlyweight extends Flyweight {
    @Override
    public void operate(int extrinsicstate) {
        Log.d("meee","具体:"+extrinsicstate+"  "+this);
    }
}

public class UnsharedFlyweight extends Flyweight{

    @Override
    public void operate(int extrinsicstate) {
        Log.d("meee","不分享的"+extrinsicstate);
    }
}

//客户端代码
        //共享的数据库
        FlyweightFactory.getFlyweight(FlyweightFactory.TYPE_1).operate(998);
        FlyweightFactory.getFlyweight(FlyweightFactory.TYPE_2).operate(998);
        FlyweightFactory.getFlyweight(FlyweightFactory.TYPE_3).operate(998);
        //私有的数据库
        UnsharedFlyweight unsharedFlyweight = new UnsharedFlyweight();
        unsharedFlyweight.operate(998);

网站范例

public interface  Website {
    void run(User user);
}

public class WebsiteImp implements Website {
    protected  String name;

    public WebsiteImp(String name) {
        this.name = name;
    }

    @Override
    public void run(User user) {
        Log.d("meee","正在运行"+user.name+"的"+name);
    }
}

public class User {
    String name;

    public User(String name) {
        this.name = name;
    }
}

public class WebsiteFactory {
    public static HashMap<String,Website> map;
    static {
        map=new HashMap<>();
    }

    public  static Website get(String name){
        Website website = map.get(name);
        if (website==null){
            website=new WebsiteImp(name);
            map.put(name,website);
        }
        return website;
    }
}

//客户端代码
        //共享的数据库
        FlyweightFactory.getFlyweight(FlyweightFactory.TYPE_1).operate(998);
        FlyweightFactory.getFlyweight(FlyweightFactory.TYPE_2).operate(998);
        FlyweightFactory.getFlyweight(FlyweightFactory.TYPE_3).operate(998);
        //私有的数据库
        UnsharedFlyweight unsharedFlyweight = new UnsharedFlyweight();
        unsharedFlyweight.operate(998);


04-12 15:33:27.332 26986-26986/com.junx.designpattem D/meee: 正在运行小黄的博客
04-12 15:33:27.332 26986-26986/com.junx.designpattem D/meee: 正在运行小张的博客
04-12 15:33:27.332 26986-26986/com.junx.designpattem D/meee: 正在运行小丽的博客
04-12 15:33:27.332 26986-26986/com.junx.designpattem D/meee: 正在运行小蚕的博客
04-12 15:33:27.332 26986-26986/com.junx.designpattem D/meee: 正在运行小黄的淘宝
04-12 15:33:27.332 26986-26986/com.junx.designpattem D/meee: 正在运行小蚕的淘宝
04-12 15:33:27.332 26986-26986/com.junx.designpattem D/meee: 2
实例只有两个