设计模式-装饰模式

个人理解: 装饰模式，是对原有功能上的一种增强。

以下情况使用Decorator模式

1. 需要扩展一个类的功能，或给一个类添加附加职责。

2. 需要动态的给一个对象添加功能，这些功能可以再动态的撤销。

3. 需要增加由一些基本功能的排列组合而产生的非常大量的功能，从而使继承关系变的不现实。

4. 当不能采用生成子类的方法进行扩充时。一种情况是，可能有大量独立的扩展，为支持每一种组合将产生大量的子类，使得子类数目呈爆炸性增长。另一种情况可能是因为类     定义被隐藏，或类定义不能用于生成子类。

UML图:

代码案例:

              一个商场收费案例。

IShopCharge：  商场收费计费接口  +charge()

ShopChargeGeneral: 无任何装饰增强，常规计费（该多少就多少）

AShopChargePrivilege: 商场收费，优惠计费抽象类  实现 IShopCharge

// 因为是在原有的计费基础上的装饰增前，所以需要，依赖注入原始计费实现。

       -IShopCharge shopCharge;

      +setShopCharge(IShopCharge shopCharge)

      //重写原有计费接口实现

      +charge(); 

ShopCharegeReturn:  商场收费，优惠返现计费实现类  继承优惠计费抽象类

        -double bCost; //返现基准

        -double rCost  //返现额

        +charge() //重写计费实现.

ShopChargeDiscount    商场收费，优惠打折计费实现类  继承优惠计费抽象类 

      -double discountNum //折扣率

     +charge() 重写计费实现

代码:

 

IShopCharge 接口

     

<pre name="code" class="html">package com.bo.decorator;public interface IShopCharge {public double charge();}

      

 ShopChargeGeneral 普通计费实现类代码： package com.bo.decorator;/** * 商场正常收费 * @author 波 * */public class ShopChargeGeneral implements IShopCharge {privatedouble money ;private ShopChargeGeneral(){}public ShopChargeGeneral(double money){this.money = money;}@Overridepublic double charge() {// TODO Auto-generated method stubreturn money;}}

AShopChargePrivilege:  优惠计费抽象类package com.bo.decorator;public abstract class AShopChargePrivilege implements IShopCharge {private IShopCharge shopCharge; public final void setShopCharge(IShopCharge shopCharge) {this.shopCharge = shopCharge;}@Overridepublic double charge(){return this.shopCharge.charge();}}

ShopCharegeReturn :返现优惠实现类:package com.bo.decorator;public class ShopCharegeReturn extends AShopChargePrivilege {private double bCost;private double rCost;private ShopCharegeReturn(){}public ShopCharegeReturn(double bCost,double rCost){   this.bCost = bCost;   this.rCost  = rCost;}@Overridepublic double charge() {// TODO Auto-generated method stubdouble _money = super.charge();return _money-((int)_money/bCost)*rCost;}}

ShopChargeDiscount :打折优惠实现类:package com.bo.decorator;/** * 商场打折消费 * @author 波 * */public class ShopChargeDiscount extends AShopChargePrivilege {private double discountNum ;public ShopChargeDiscount(double discountNum){this.discountNum = discountNum;}private ShopChargeDiscount(){}@Overridepublic double charge() {// TODO Auto-generated method stubdouble _money = super.charge();return _money*this.discountNum;}}

TestMain :测试类package com.bo.decorator;public class TestMain {public static void main(String[] args) {IShopCharge  shopCharge = new ShopChargeGeneral(300);double money = shopCharge.charge();System.out.println("常规收费: "+money+"$");//满一百返十块AShopChargePrivilege shopChargePrivilege = new ShopCharegeReturn(100,10);shopChargePrivilege.setShopCharge(shopCharge);money = shopChargePrivilege.charge();System.out.println("返现优惠后，收费: "+money+"$");//打折AShopChargePrivilege shopChargeDiscount = new ShopChargeDiscount(0.8);shopChargeDiscount.setShopCharge(shopCharge);money = shopChargeDiscount.charge();System.out.println("打折优惠后，收费: "+money+"$");}}

输出:常规收费: 300.0$返现优惠后，收费: 270.0$打折优惠后，收费: 240.0$