享元模式

享元模式

介绍

享元模式使用共享来避免大量拥有相同内容对象的开销，避免内存的损耗。享元对象能做到共享的关键是区分内蕴状态和外蕴状态。（结构型）
内蕴状态是存储在享元对象内部的，不会随环境的改变而有所不同（内蕴状态可以共享）。
外蕴状态是随环境的改变而改变的，不可以共享，外蕴状态不可以影响享元对象的内蕴状态，它们是相互独立的。

优点

• 大幅度地降低内存中对象的数量

缺点

• 使得系统更加复杂
• 享元模式将享元对象的状态外部化，而读取外部状态使得运行时间稍微变长

结构(涉及角色)

• Flyweight：抽象享元角色，规定具体享元角色要实现的方法。
• ConcreteFlyweight：具体享元角色，实现抽象享元规定的接口。
• FlyweightFactory：享元工厂角色，负责创建和管理享元角色。

DEMO

抽象享元角色，抽象享元中接受一个参数state，state是外蕴状态，由外部传入的不可被共享。

package factory.pattern.flyweight;/** * Created by FK on 2017/8/1. */public interface FlyWeight {    public void operation(String state);}

具体享元角色，内部intrinsticState是内蕴状态，内蕴状态在被对象创建后就不会在改变了。

package factory.pattern.flyweight;/** * Created by FK on 2017/8/1. */public class ConcreteFlyWeight implements FlyWeight {    private Character intrinsicState = null;    public ConcreteFlyWeight(Character intrinsicState) {        this.intrinsicState = intrinsicState;    }    @Override    public void operation(String state) {        System.out.println("Intrinsic State = " + this.intrinsicState);        System.out.println("Extrinsic State = " + state);    }}

享元工厂类（客户端不可以直接将具体享元类实例化， 必须通过一个工厂对象得到享元对象）

package factory.pattern.flyweight;import java.util.HashMap;import java.util.Map;/** * Created by FK on 2017/8/1. */public class FlyWeightFactory {    private Map<Character, FlyWeight> files = new HashMap<>();    //享元工厂在系统中只有一个，可以使用单利模式来获取        private static FlyWeightFactory flyWeightFactory = new FlyWeightFactory();    private FlyWeightFactory(){}    public static FlyWeightFactory getInstance(){        return flyWeightFactory;            }    public FlyWeight factory(Character state){        FlyWeight fly = files.get(state);        if(fly == null){            fly = new ConcreteFlyWeight(state);            files.put(state, fly);        }        return fly;    }}

测试：

package factory.pattern.flyweight;/** * Created by FK on 2017/8/1. */public class Test {    public static void main(String[] args) {        FlyWeightFactory factory = FlyWeightFactory.getInstance();        FlyWeight fly = factory.factory(new Character('a'));        fly.operation("first call");        fly = factory.factory(new Character('b'));        fly.operation("Second Call");        fly = factory.factory(new Character('a'));        fly.operation("Third Call");    }}

代码都在github上，地址是fk5431
https://github.com/fk5431/designPatterns